If you say this chapter should be Chapter 3.5 in Wheels, why not rework your story and fit this in? It doesn't feel like you'd need to do any changing to make it fit except the hassle of deleting and re-uploading the chapters.

This chapter reminds me of how Ling is so laid back and serious at the same time. He had his body stolen by a Homunculus and eventually made friends with said thieving monster so that they came to share. He takes this experience entirely in stride. And now Ling is considering returning to that setup with the help of that Homunculus's sister and lover. And the way this is arranged, it's entirely possible for Greed (in control of Ling) and Envy (in control of Lan Fan) to have sex, with the ironic part being that Ling and Lan Fan might not mind that so much if only they were the ones choosing it.

I don't know what you meant by "Wrath killing his host". Do you mean Wrath was originally like Greeling but the Sin killed the human Wrath was before becoming a Homunculus? I've never thought about it that way.

The missing confrontation between Envy and Lan Fan in the manga is definitely an important thing for your story and I like the recognition of Lan Fan's besting Envy from that scene and Envy getting a revenge of sorts by taking her over now. Wrath and Pride's surprise and wariness over the Xingese ability to detect the Homunculi demonstrate that they've never had difficulty that way before and it would make Envy particularly vulnerable.

Now this idea is one that could be used to good effect as a jump-off for a larger, developed story. And I like it because it's entirely plausible for Greed to catch up to Ed and the others in the tunnels rather than right before the peak of the eclipse to interrupt Father's transmutation. Outside of your canon, it's harder to make Greed rescue Envy, but I wouldn't find it impossible. His Ultimate Shield should be able to protect him from Mustang's flames, and although Greed fights with the other Homunculi, the fight with Pride and Gluttony was mostly self-defence and the fight with Wrath was personal. He didn't defect the first time because he wanted his siblings to die, but merely to be free from serving Father's interests rather than his own. So I find it conceivable that Greed would object to just standing by and watching Envy die regardless of whatever type of past one envisions for them.

I would object to Mustang identifying Greed as a Homunculus right away. I don't think they had met before so that Mustang would know who Greed was... Unless he's guessing based on his Sin name, which, as we discussed before, is a tricky point with Amestrian language and history.

I would also say that only the very ending really gives us the cute fluff you were aiming for. It's almost all serious until the last few paragraphs.

I love the insight into Envy's thoughts in this chapter. It's such a small scene, really. It doesn't feel like there should be enough to justify exploring one character's point of view here, but I really feel like you hit a lot of good points. That Envy would be a little hurt that Father didn't care at all about it, even after exploding from Gluttony's stomach. (I suppose, though, that Father didn't know yet that Envy'd been eaten, and so even if he could have had concern, it didn't have the time to develop.) The train of thought over Wrath making them think that Lust had die- no wait, "wasn't coming back." The (what I find very hard to imagine) idea of Lust being in a male body. It's a lot of small ideas that still fit in nicely into a small but not overpacked scene.

As I do remember promising to review this some long time ago...

I think the first time I read the first chapter, I found the flow to be confusing, but with a second read, I followed it much more easily. It's certainly an interesting technique to alternate between present and past with basically no breaks at all. Of course, being me, I wish there wasn't the sexual references (even though you've not said anything graphic), but I'm not saying that to change anything you've written. I'm just sort of throwing it out there because this is a review and I have to say something.

The thing that jumped out as most insightful is the comments about Pride being 'stuck' in his child body. Instantly the thing I was reminded of is "Interview with a Vampire" by Anne Rice. (And if you ever want to read a story about vampires, as far as I'm concerned, Anne Rice is the only author worth reading.) Spoiler alert: In the story, a child vampire is created and a fair part of the plot discusses the wrongness of what the main character considered an act of charity at the time (for the child would have died of illness had she not been 'rescued'). This child vampire does not grow up; her mind matures into a woman but her body remains small and weak and incapable of sex and she hates her creators and herself for it. If I accept your cannon as true, Pride is in the exact same situation and the play on jealousy and pride and shame is appropriate. I especially like the way Envy is able to attack Pride's form. You said you thought Envy liked its "Envysaurus" body. I rather think Envy was ashamed of its inhuman form, but either way, before this chapter, I considered Envy to be alone in having an abnormal body. To realize that Pride could also resent the form he's in is a nice thing to have pointed out.

I like the conversation here, most of it feels very much in character. Also, that's a really exemplary way to bring up how dependent Envy is of the shapeshifting and how much it bothered it that Lan Fan could just identify it right away.

That last line is great!

Very nicely done. Very emotional chapter. You capture Envy's voice so perfectly, I felt so bad as she remembered all the times she was beaten. Also, what a great stinger line to end on! As always, I look forward to more!

Ooh, interesting, another take on how Envy could survive. Sure is fluffy! Scar seems more cooperative than I'd think.

I'm still alive! X)

This first chapter was nice, I liked how Envy put a foot in Pride's mouth. (I'm hoping putting a foot in someone's mouth is the correct saying here.)

Following the actual actions and dialogue was a bit difficult since it jumps around, but it was so short that it wasn't that much of an issue.

I really liked this, the whole scene around Mustang's confrontation with Envy is positively ripe for alternate interpretations and Greed showing up like this is one I hadn't considered, love the way you handle it. Definitely a case of author jealousy now, wish I'd thought of this first. As always, can't wait for more!

Expanding on existing scenes from the show has always been one of my favorite forms of fanfiction, across all media. Just because within the context of most works they rarely leave time or reasoning to expound on every character's thoughts and feeling at any given time and what exactly would be going through Envy's head in this scene has always intrigued me, and this felt very authentic and added a lot to the scene, I'll probably hear Envy thinking all this every time I watch it now :) and the idea that Envy had to take over Greed's role amuses me, also this scene has given me a plot bunny for a Ling!Lust, but more on that later... I enjoyed this greatly, makes me want to read more Wheels! Can't wait to see more.

Heheheh ohhh the amount of Pride analysis here is actually staggering. Envy as usual manages to hit it right on the dot - and I love how Envy is lost in the memory of pissing somebody off while having sexytimes. *face-palm* Sexy times are sexy times, En.

A really really strong start, I'm excited to see where these themes go! Man, I need to do these XD

Very nicely done, I love the format here, shifting perspective can be tricky but you pulled it off really well for this. Envy driving Pride crazy was an absolute joy to read, I love the way you write him, he's so often one of the neglected homonculi, the idea of him being jealous of Greed amuses me greatly and makes a lot of sense. So glad I got see your first of these themes so soon!