PROMPT 5: Since Zenitsu's birthday is really near, 3rd September, maybe something related? Like it's not a special day for Zenitsu but Tanjirou wants to make Zenitsu happy in his birthday, the day he came to the world, because he's so happy to have met him and can't believe a world without him?

"Tomorrow's your birthday, isn't it?"

Zenitsu looks up from where he nearly collapsed on the ground, ropes tied tightly around his shoulders. With each step he took, the boulder he carried left a trough in the dirt. At the top of said rock sat the very figure who asked. "Yeah, but what does that have to do with anything?"

"We should celebrate-" The old man cuts himself off in exchange for whipping out his stick and landing a solid blow to the back of the black-haired boy's knees. He yelped abhorrently. "Legs straight! I'm not getting any younger, Zenitsu! We still have a mile left to go before we reach home!"

Well that just right pissed Zenitsu off. "GRAMPS…! Before you talk about celebrating, why don't you consider my health for a second?! This training is hell! I'm living in hell on earth. I'm thirsty and hungry. I feel my life flashing before my eyes! I won't LIVE UNTIL TOMORROW AT THIS RATE, and you're asking me to think about my birthday?!"

And there goes another whack this time on top of a dark nest of hair. "If this level of training is enough to kill you then you're better off dying now rather than on the battle field."

"SO MEAN…! WHAT THE HELL, GRAMPS?!"

"STOP CALLING ME GRAMPS!"

They do make it home without anyone dying, much to Kuwajima's approval and Zenitsu's horror that this only meant his inevitable end would be even more gruesome. Both retire for the night without his birthday being mentioned again. Zenitsu thought that was the end of that topic. But when he woke up bright and early out of habit for his morning training, adorning a plain blue haori, he ends up nearly kneeling over when what awaited him on their tiny tatami mat isn't a wooden sword but a cake. A ring of peach slices brighten the top like a beacon.

Zenitsu gaps. Kuwajima grins, patting the spot next to him. "Come eat your treat, boy! I spent all morning preparing it and I'll be damned if we leave this room without singing a happy birthday for you. Don't forget the wish and gifts. That's the most important part!" Before he can even react, Gramps whips out something from behind his back.

It's a haori, one matching the old man's very own with triangles decorating it in patterns but in a shade of bright yellow.

"G-Gramps…" He's speechless. He's utterly speechless and doesn't know what to do with himself when he feels that familiar sting behind his eyes that indicate tears. However, his old man answers that question for him when he stands. Kuwajima struggles a little, whether physically or mentally, to wrap his arms around the taller and sobbing child.

Zenitsu knows it's stupid but in that moment, he's happy. Gramps always had the sound of a crackling fireplace. It was rustic and old but still strong.

"There, there, Zenitsu." Wrinkled fingers pat his back. "What's wrong?"

"N-Nothing…!" What he doesn't say remains in his head; that his memory can't even go back far enough to when he was able to sit at a table and eat cake with family. The best that living on the streets could offer was a small leftover loaf of bread handed to him by bakery owners out of pity. The most comfort as an orphan that he got came from the neighborhood stray cats. For the life of him, Zenitsu can't remember the last time anyone sang happy birthday for him.

Kuwajima senses the mood. He isn't pleased at his student's sworn silence but doesn't push it. Instead, the old man opts to distance himself from the other enough to give him a right threatening glare. "Boy, you better promise me something."

"What is it…?"

"Promise me that you'll never celebrate your birthday alone anymore."

"What are you talking about, Gramps…?" Zenitsu lets out a little giggle past the tears. He quickly wipes them, breathing his snot back in ungracefully. No matter how much he complains, he likes listening to that fireplace. "That's not necessary at all! I have you."

His Gramps hums, smiling in a way that the Zenitsu from back then didn't know held any sadness. "True. I suppose that you do."

Looking back on it, Zenitsu wonders if his old man knew what was going to happen. He wouldn't be surprised if he did. Kuwajima's biggest weakness was his gullible heart and kind sound that took in any stray that he saw potential in. He dedicated his life to them. Zenitsu never met someone as giving and sacrificial as his Gramps. Otherwise, the old thunder pillar was sharp as a blade and strong as a strike of lightning.

"Tomorrow's your birthday, isn't it?"

Gramps…? He shoots his head up from where it was staring silently at his rice bowl. But the image of his gramps, proudly seated on a rock is nowhere to be found. The vision fades, and what he sees instead are the gentle amber eyes of Tanjirou. "H-Huh…?"

Tanjirou hums. And when his next words echo exactly as Kuwajima's, Zenitsu feels a tinge of pain behind his eyes. "We should celebrate."

The blond gulps his food down, sighing. It was a coincidence. He was paranoid. He was just thinking too much about it. "What did you have in mind?" He says it but doesn't sound so much excited more than tired.

"We didn't have any time to prepare since we just got back from a mission." Tanjirou notices the lackluster mood but smiles anyway, trying to liven the air. "But I've done this for my brothers and sisters before. I don't mind getting up early tomorrow to bake a cake. Inosuke could go into town and buy some candles. I'll even ask Nezuko to set the table! We could sit around it and sing happy birthday. Don't forget the wish and gifts, too! That's the most important part."

All of a sudden, Zenitsu felt sick to his stomach.

"Don't."

The sound of Tanjirou snaps nearly shut, lowering into a tirade of sadness. He feels horrible, especially when good and kind-hearted Tanjirou looked so delighted at the prospect of celebrating someone else's birthday. He's a good guy, an idiot, but a really good person. At this moment, though? Zenitsu couldn't explain that lurch in his gut as anything but a burning desire to see his Gramps again. "I have plans to go somewhere tomorrow."

His friend tilts his head. Rather than leave it at that though, Tanjirou huffs in a pout. He slams his chopsticks down on the counter, not even flinching when Inosuke silently steals another stick of tempura from his plate. Indignant is what he sounds like, and Zenitsu doesn't know whether to be grateful or frustrated at the melody. "Great. We'll all come with you."

"Thanks, Tanjirou, really." They're words that he's said to him twice now. Perhaps if Zenitsu repeated them, he'd know when to take a hint. "But this is something that I have to do on my own."

Rather than relent like before though, the sun breather does the unthinkable and increases the intensity of his worry tenfold. His pout now transcends into concerned anger. "Oh no. Not this time, Zenitsu! I know sometimes that you have to do things on your own. I let you go before but there's no way I'm letting you celebrate your birthday alon-"

"I won't be alone." Zenitsu snaps before Tanjirou can finish his sentence. Despite the front though, the only word that's running through his mind is similar. What Tanjirou was spouting was much too similar to his Gramps and he couldn't stomach hearing the rest of his statement. The other seemed crushed, so Zenitsu reassures him. "I promise."

Given, buying two cheap pastries at the local market and laying one in front of a gravestone wasn't exactly not being alone either. Knees on the concrete and the rest of his body seated on top of his calves, Zenitsu held both hands together in prayer. "Hey, Gramps. How have you been?"

He doesn't get a reply, of course.

"I've been practicing seventh form more. I think I'm getting the hang of controlling it better."

"I tried that red-bean mochi from the vendor that you really like for the first time ever. It's all right, I guess. The paste is a little dry and too sweet though. I can see why you kept raving over the texture. It was perfect. But you still made it better."

There's a weight in his heart. He doesn't know what it is.

"So get this…! The other day, I saw Tanjirou walking by and holding his sword really funny. I asked him what happened, and he has the nerve to tell me that he chipped it! He needs to stop doing that! Did no one teach him how to handle a blade so it wouldn't break? You'd have my head if I ever so much as dented my sword, Gramps. You said so yourself! And you know what? I haven't broken it once. Maybe that hellish training was worth it."

He's rambling. Zenitsu knows he's rambling. It's a hot autumn afternoon and the icing on the pastry is already melted into a sticky mess. It'd be gross to eat it now. Still, the blond takes the tiny confectionary in one hand and stuffs the entire thing in his mouth like it's his last food source. The sun is beginning to set but he doesn't feel ready to leave.

Maybe he fell asleep at some point in that position. Maybe he was too up in his head space to notice, but it isn't until there's a soft gasp from behind him that Zenitsu whips around in surprise. It's Tanjirou. Crate carefully held between two arms, eyes trail the gravestone in silent and horrified realization. He's quick to apologize. "I-I'm so sorry, Zenitsu. I followed your scent here. I didn't know."

Rain, there's rain in his soul. Tanjirou is upset- what, he shouldn't be feeling that way! Stop it! Stop it right now! I should be the one who's upset around here!

But the fact of the matter was that Zenitsu wasn't. He doesn't feel embarrassed or even angry at being caught, but weirdly relieved at seeing him. He shoots out of his spot, that heaviness in his heart dissipating the slightest. He's quick to grab the boy's cheek and pinch it out, anything to get rid of that sad expression. "Yeah right, you didn't know…! I told you that I had to do this on my own, yet you followed me here anyway?! I know you're worried but that's just STUBBORN! You're a stubborn idiot, Tanjirou! I'm sure of it!"

The other cringes, feeling ashamed. He manages to mumble past his stretched left cheek. "I am."

"SAY IT…!"

"I am a stubborn idiot."

"GOOD." Zenitsu finally lets him go, but Tanjirou doesn't seem any happier. On the contrary, one listen to his music is all it takes for him to decipher that the brunet is close to tears. "H-Hey…! Why are you crying? Cut that out. I'm not mad at you!"

"You should be, I think." What kind of response was that? The blond didn't understand, so Tanjirou hurries to wipe his wet eyes but to no avail. More water simply forms. "Because even though I apologized and would agree I shouldn't have come, I don't regret it at all. I'm so glad that I did. I would do it again."

"HAH…?!" Okay, now Zenitsu was mad. "No, that's definitely not what you should say! Besides, it's just a dumb birthday. There's nothing to get all emotional over! You should turn back around now, admit the error of your ways, and never do it again! That's how responsible adults handle making a mistake, Tanjirou. Just do that and I assure you that I'll forgive you!"

"No." Tanjirou puffed out his cheeks. It looked ridiculous combined with the tear tracks on his face.

"ARGH…!" All he could do was screech in response. "I DON'T GET IT…! You're impossible! You're a child! I don't understand you at all! Why on earth are you like this?! I can feel ten years being shaved off of my life span-!"

"Zenitsu." It's amazing how much that name being uttered from this one person managed to make the blond take pause. Tanjirou doesn't look any more willing to admit defeat. He's still indignant, practically yelling his words like he was trying to personally attack Zenitsu with them. "I- WE'RE ALL HAPPY TO HAVE MET YOU! That's why your birthday isn't dumb! Don't call it that, please!"

"Did you just say please?! Oh my god, you're so bad at this arguing thing!"

"I'm not good at being angry with people I care about. Does it matter how well I do anyway?! What's important is that I get my point across and you know how much you mean to me!"

"WHA-?!" His cheeks burn red. "Y-You don't mean that!" Zenitsu knows he does.

"I do! If you weren't born… if you weren't here, so many of us wouldn't be where we are today. You don't have to celebrate by yourself anymore. You have me. You have Inosuke. You have Nezuko too. Genya and Kanao would gladly join in. All of the other pillars would wish you well. I'm glad I came because then I can tell you this."

There it was again. Those words hurt in a way that wasn't necessarily bad. And past his vision, he can hear the slightest hint of a crackling fireplace around them. Gramps…? When Tanjirou offers the box in his hands, the addressed accepts it. Golden eyes peer at him in question but all his friend does as any form of explanation is wipe at his wet face again and smile.

"Happy Birthday."

Zenitsu opens the box. It's a homemade cake decorated with peach slices.

Oh.

Oh.

Tanjirou, you idiot…!

You win this time.

Taking the victory that they both knew he had in stride, Tanjirou holds out a hand in offering. The tears still aren't quite gone from his amber eyes. Yet, his melody is serene. "Let's return and eat it together with everyone."

Zenitsu reaches out to take that hand, and gasps when he feels the gentlest nudge pushing him forward.

Go, boy.

He turns around but no one is there.