Author's Note: This story is a follow-up to the story arc in my previous fanfics "The Girl Next Door," "Donatello's Demise," and "Aftershock." My canonicity is basically plausible up until right before the episode "The Good, the Bad, and the Casey Jones," and from that point on it deviates significantly from the show. If you don't want take the time to read the three previous stories, or if it's been a while since you read them, here is a detailed synopsis of them. ALSO: This is an incomplete story because I just couldn't finish it. I have, in the last chapter of this, included an outline of how I was planning to wrap the story up. So if you still want to read, that's great and I appreciate it, but for fair warning's sake this may not be the most satisfying experience for you. I apologize. My life has been falling to pieces and I'm just trying to pick them up. I hope you can understand. If you want complete stories please read the first three fics leading up to this, you may find them to be satisfying.

Disclaimer: Teenage Mutant Ninja Turtles, all related characters, and all derived works are the intellectual property of Nickelodeon, Viacom, Eastman, and Laird. This story is for entertainment purposes and not for monetary gain. In no way should this story be taken to be anything other than a fan-based expansion of and commentary on the original work. n00btmntfan is in no way associated with the makers of TMNT.

In "The Girl Next Door," a Japanese woman named Satou Atsuko moves into the apartment directly downstairs from April. Satou is a computer programmer, collector of traditional Japanese weapons, and an avid disciple of ninjutsu. After an unfortunate encounter with April's mutated father, Atsuko befriends April. April, who is struggling with being torn between Donnie and Casey, confides in Atsuko more and more. However, unbeknownst to April, Satou Atsuko used to go by a different name—Tang Mei. Tang Mei was the older sister of Tang Shen.

Shredder and Splinter, it turns out, had made a childhood pact when they were in school: Splinter, who was enamored with Tang Mei, and Shredder, obsessed with Tang Shen, agreed that they would help each other win the object of their affection. However, Tang Mei ended up marrying a man named Kobayashi Kenshin. Splinter accepted this and moved on—only to discover that Tang Shen had loved him the whole time. When Tang Shen chose Splinter, Shredder saw it as a violation on Splinter's part of their childhood contract. When Shredder finally decided to finish Splinter off, he decided to make Splinter suffer first. So, he captured the Kobayashis and made Tang Mei watch while he killed Kenshin and their sons Kenji and Suki. Then, he planned to capture Splinter and make him watch while he raped the woman who had once been the object of Splinter's affection. However, when Shredder failed to capture Splinter (thinking him dead in the fire), Shredder dealt with his anger by repeatedly raping Tang Mei over the one year he kept her prisoner.

After she had been captive for a year, Tang Mei managed to escape. She changed her name and sought a new life, devoting herself martial arts and learning advanced computer programming. Years later, she gets a job offer in New York and moves there—into the apartment below April's.

Donnie is working on a supercomputer to help him find the retro-mutagen, and April hopes to enlist Satou's help in the matter. However, April's life is complicated by the triangle she feels stuck in with Donatello and Casey. On the one hand, Casey makes her giddy with excitement and she really likes him (plus, there is the bonus of his not being a giant turtle), but on the other, she feels that she owes Donnie for all of the things he has done for her since they met. Eventually, after much agonizing over it, April ends up dating Casey—however, their relationship ends up being rather short-lived.

The day after Casey and April become an "item," Casey is captured by Karai, who has learned of Casey's own sordid past. As a recovering alcoholic, Casey is very vulnerable to relapse. Using that against him, Karai asks him to help her capture April. Unable to resist the alcohol, Casey agrees to help her in exchange for satisfying his addiction.

Eventually, Satou figures out that April is connected to Splinter—whom Satou partly blames for Tang Shen's death as well as her own torment at Shredder's hands. Satou is with April when the Foot Clan, using Casey's tip, track April down. Satou thinks that April is part of a trap set by the Shredder, and wanting to escape she ends up knocking April out—who is then promptly taken away by Karai.

Satou realizes her mistake and manages to find the turtles using April's t-phone. The turtles think that Satou is with the foot—and by the time they figure everything out, it's almost too late. The turtles then rush off to save April, leaving Satou and Splinter alone in the lair. Satou and Splinter reconcile.

Meanwhile, Shredder is planning to rape April as another way to punish Splinter. He almost does, but then the turtles burst in to save the day. Michelangelo is grievously injured and April is severely traumatized; however, it is unsure whether Shredder survived the encounter.

When Satou and Leonardo go to find Casey, they discover the truth. They give Casey two days to either tell April himself or to just break up with her and never speak to her again. Casey is too ashamed of the truth and so he chooses the latter option. Donnie, who learns the truth from Leo, decides that April deserves to know the truth too, since she is so upset by Casey's mysterious dumping of her.

Furthermore, April has started to suffer from PTSD; her father is the only psychologist who will believe the strange situation is true. Donnie doubles his resolve to fix Mr. O'Neil so that Kirby can help April recover. Donnie swears to April that he will never rest until he finds a cure. Then, to his surprise, April declares that she loves Donnie and they kiss.

The story ends with Satou Atsuko reclaiming her identity as Tang Mei. The turtles adopt her as their aunt. She decides that she will finally heal from her old traumas and resolves to help April overcome her PTSD.

In "Donatello's Demise," we see April and Donnie's relationship off to a rocky start as she goes through PTSD and he works feverishly to perfect the retro-mutagen. Mei still feels a little unsure about who she is, but spends a lot of time with her new family, and steadily makes peace with her past. She helps April with coping and assists Donnie with his super-computer project so that he can develop the mutagen.

At Michelangelo's suggestion, Splinter asks Mei if she would like to move into the lair with them. Mei thinks about it for several days and then agrees. The super-computer is finished, and now Donnie can work on the retro-mutagen in earnest.

Things take an unexpected turn when April is approached at school by Casey, who has finally decided to stop avoiding her and tell her the truth. Unfortunately for him, April already knows, and she is furious with him. Nevertheless, talking with him triggers a panic reflex in April, and she spends the rest of the day terrified that this is all a ploy so that Shredder can get a hold of her again. The symptoms of her PTSD and this fear make her lose control, and she ends up going to her apartment and tries to kill herself by slitting her wrists.

She is found later that evening by Mei and Donnie, who rush her back to the lair. She has lost a lot of blood, and because of her unique DNA, there is nobody in the city who could be a proper donor. Donnie breaks down, out of ideas – fortunately, Mei steps up to the plate and suggests that they use Donnie's equipment to synthesize blood for April. They are successful, but April is in a coma for seventeen days.

During that time, Donnie perfects the retro-mutagen and they test it on a hostile to see if it works on a complete organism. After turning Fishface back into a human, they realize that it's totally safe and plan to use it on Kirby.

After the test run, the turtles get back to the lair to find April awake. Everyone is ecstatic, except that Donnie has an unexpected reaction of anger at first. After a while, he is able to forgive her, and for a little while, it looks like everything will go back to normal.

Then, when Donnie and Mei are trying to administer to retro-mutagen to Kirby, Donnie accidentally injects himself with it and gets turned back into a regular turtle. Splinter withdraws from everybody; Mikey has a spectacular breakdown.

Unsure of what to do and unable to turn to Splinter for help, Leo steps up to the plate and decides on a course of action. He decides that they will use Karai to communicate with the Kraang for them, since the Foot and the Kraang are sort of frenemies. To reach Karai, they decide to use Casey.

Unbeknownst to them, Karai has been having dreams about Mei ever since she first saw her – she doesn't know who Mei is, but feels like she should know her. She offers Casey anything he wants in exchange for more information about Mei, but he refuses to help her. Nevertheless, she leaves him with a number "just in case," and he finds himself unable to throw it away.

When the turtles approach him, Casey provides them with the phone number and they contact Karai. The plan is set in motion, and Karai begrudgingly agrees to help them. However, Shredder's scouts have gotten pictures of Mei. He explains to Karai who she is, lying and saying that Mei's husband helped Splinter kill Tang Shen. He explains how he killed Mei's husband, and that Mei is probably looking for revenge. Furious, Karai promises that she will capture Mei so that she will no longer pose a threat.

After setting up a trap for Mei and capturing her, Karai refuses to listen as Mei tries to tell Karai who she really is. Karai believes she is lying and ends up delivering Mei to Shredder, but Karai feels incredibly guilty and doubts herself.

Shredder, being the terrible excuse for a human being that he is, gloats over Mei and asks her where he can find Splinter and the turtles. When she refuses to help him, he beats her and the scene cuts away, but it is obvious as to what is happening. In the meantime, Baxter Stockman is hacking into Mei's phone, and is able to trace the location of the lair from there.

When Mei's phone is hacked, it sends out an automatic distress signal with coordinates. Kirby, who has been un-mutated, helps them figure out where to go – Shredder's lair. Splinter, Leo, Raph, and Mikey rush off to the rescue, leaving April, Kirby, and Donnie in the lair. Kirby has purchased a gun off the black market so that he can protect April; when April points out that guns are illegal in New York City, Kirby quips that so are sodas larger than 16 ounces.

While Splinter and the turtles arrive at Shredder's lair and rescue Mei, they discover that Shredder has already left and has gone to the lair. Splinter sends the turtles ahead and he stays behind to help Mei escape.

Shredder and Karai arrive at the lair and find it deserted. They venture in slowly and hear a gunshot. Karai sees April in the dojo and runs in to capture her, while Kirby keeps shooting at Shredder (and missing.) April and Karai struggle – Donnie helps by biting Karai on the Achilles' tendon, and when she is thrown off balance, she bumps into the picture of Splinter's family. She has the horrible realization that Mei was telling the truth.

Leo, Raph, and Mikey arrive at the lair and immediately attack Shredder. Hearing sounds coming from the dojo, Leo runs in and finds Karai staring at the picture. He asks if she will help them. She says she will, but only if she gets to kill Shredder. They all head back out into the main lair, where Shredder is unfortunately gaining the upper hand. Sometime during the fray, Kirby gets thrown across the room and lands next to the turnstiles; his gun lands next to him.

Splinter arrives just in time to get everyone out of a sticky spot, leaving Mei near the turnstiles. However, Shredder grabs hold of Karai and threatens to kill her unless they let him leave.

Mei grabs Kirby's gun and fires twice. The first shot knocks off Shredder's helmet; the second kills him.

Afterwards, Kirby and April take Mei to the hospital, since none of them have the expertise to treat her extensive injuries. When April and Kirby return to check on everyone, they report Mei's injuries. Karai asks to talk to April, and April extends a hand of friendship, much to Karai's surprise.

They all put together a 'welcome home' party at Mei's apartment. Karai finally gets to talk to Mei again, and she is shocked when Mei forgives her.

Karai decides to return to the Foot Clan to work under cover to tear the rest of the Foot Clan down as well as try to get help from the Kraang.

The story ends with April promising Donnie that she will wait for him, no matter how long it takes.

(Oh yeah, and something I forgot to mention during this synopsis is that Mei and Splinter sort of kind of might be forming a relationship - they know they care about each other in more than a familial way, but it's complicated.)

In "Aftershock," Mei, April, and Kirby continue research on a way to re-mutate Donatello, while Karai goes to the Kraang for assistance. After learning that they cannot duplicate a mutation exactly, but can get very close, they decide to enlist their help. Meanwhile, a new villain enters the scene in the form of Oroku Daiki, the man who calls himself 'the Ronin' and who is next in position to take over the Foot Clan. He makes Karai swear her allegiance to him, after revealing that he knows Splinter is her true father. He had been there on the night that Shredder attacked Splinter's home, and watched as Karai was taken from the rubble.

Karai reports this to the family, and she returns to Shredder's old lair with Leo, Raph, and Mikey in tow to protect her. However, when they arrive, she betrays them by gassing them and tying them up, then delivering them to the Ronin. The Ronin tells Karai that he will exterminate everyone in the Hamato bloodline down to the fifth generation, wherever they might be in the world. He instructs Karai to have the Kraang develop the necessary technology to assist him in this, then tells her to kill the turtles. Karai goes to attack Leo, but he uses her attack to cut the cords binding his feet, then kicks her and knocks her unconscious. He retrieves her tanto, cuts the bonds on his wrists, and proceeds to free his brothers. After a fight which none of them escapes completely unscathed, they return to the lair where Splinter treats their injuries.

Shortly thereafter, Karai shows up to return the turtles' weapons to them. They are all furious, especially Raph and Leo. She explains she was only trying to win the Ronin's trust, and that she wasn't going to actually tell the Kraang to do his project. She was only buying time until the Kraang could finish their serum to fix Donnie. Leo is not mollified.

During all of this, Mei is struggling to recover from all the injuries the Shredder inflicted on her, especially the psychological and emotional trauma. She is confined to a wheelchair while a fracture to her pelvis heals. With help from Kirby and Splinter, she begins to recover mentally. Her relationship with Splinter deepens. While she studies the information the Kraang gave to Karai, she uncovers something that could possibly help with a cure, but is unsure what to do with the information.

Finally, the Kraang have finished their re-mutation serum and they give it to Karai, but only on the condition that she deliver April to them. April agrees, and so they stage a kidnapping and Karai brings April to the Kraang. Once she is captured, April discovers that the Kraang are in fact working on Ronin's project. She destroys the computer that has her DNA information on it and then escapes the Kraang facility with the help of the turtles. They confront Karai, who says that the Ronin must have gone behind her back and spoken to the Kraang directly.

In reality, Ronin threatened Karai's life if she would not go to the Kraang, so she did, keeping it a secret from everyone else and hoping she could destroy the project before it was too late, with no one being the wiser.

They test the re-mutation serum on Xever, whom they had previously tested the retro-mutagen on. The re-mutation is a success, so they proceed to apply it to Donnie.

It fails. While Donnie is restored to himself physically, mentally, he is still absent. They can't figure out why, except that maybe since Xever was sentient to begin with but Donnie was not, this is why they cannot duplicate the results exactly. Everyone is crushed, but Mei vows she will find a solution.

Since they were counting on Donnie's help to destroy Ronin's project, they have to turn to Mei for help, who has just finally gotten out of the wheelchair. The whole gang goes to TCRI to wipe the project out.

Once there, they are attacked by both Kraang and the Foot. Raph thinks Karai is responsible and has betrayed them again, but Karai points out that these are Ronin's men, and she doesn't command them. During a fight, she takes a throwing dagger in the chest to save Raph's life, and he finally trusts her.

Finally, the Ronin joins the fray, knocking everybody unconscious except for Leo, Karai, and Splinter. He and Splinter fight, and Splinter emerges victorious. However, Karai is in really bad condition and so they have to take her to the hospital. Mei still needs to destroy the technology, and Leo goes back to help her while the others escape. The others are waiting for them when an explosion goes off in the building.

Leo and Mei do not come out.

Karai is in such bad shape that they rush her to the hospital, where April and Casey take her inside. The others return to the lair to treat their injuries, worrying about Leo and Mei the whole time.

Leo and Mei have managed to destroy the technology by blowing it up, and escape down the elevator shaft before the explosion goes off. Once they have finally reached the sewers, they have to take the long route home. They finally make it to the lair, and there is much rejoicing.

After recovering from all of this, a new development takes place. Donatello temporarily comes out of his coma-like state and highlights something on the computer, which Mei is able to, seven months later, figure out and apply to him. It works, except that Donatello's emotions don't come back. Three months pass, and they still aren't back, and he and April break up because she's convinced he can't love her anymore. She tries to rebound with Casey, who turns her down and announces he's moving to South Dakota with his foster parents.

Two years later, when April and Karai are almost 20 and the turtles are almost 19 (give or take), Leo and Karai get married. Splinter proposes to Mei, and she accepts. April and Donnie get back together, and the first glimmer of something resembling an emotion comes back to Donnie's mind just as the story ends.

(Please keep in mind that this is a 1000 word synopsis of a 100,000 word story, so a lot of detail is missing. But this should be enough for you to get the gist of what's going on.)