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As soon as Tanjirou sees the pup, he knows he needs attention and love. The omega can't help it, he loves children, he always feels an inevitable urge to protect and take care of them and Senjuro Rengoku is not an exception.
"Hi! I'm Kamado Tanjirou and I'll be living with you so I can train with your brother, is that alright?" He releases a calming scent to let the beta boy know he means no harm and just wants to be his friend.
Kyojuro smells it and inevitably relaxes next to him; Senjuro does that too although he's obviously not used to being asked such questions.
"Of course, I-I mean if my brother wants to."
"I just want to make sure you're comfortable with me around. It's okay if you're not..." Tanjirou assures him, surprising both brothers.
"It's fine," the little boy mumbles and Tanjirou feels relieved when he smells sincerity in his scent. "I like you."
"I like you too," when he turns around to ask Kyojuro where he's going to sleep, he notices that the alpha has been staring at him intently; there's a glimmer in his eyes that Tanjirou can't quite understand and it doesn't help at all that the alpha's strong, fiery scent is a little bit sweeter now.
It confuses him for a moment.
However, he decides not to question it and instead follows the alpha to his new room.
***
He keeps an eye on Senjuro because the pup looks a little bit sad sometimes; it doesn't help that his father roams around the residence with a bottle of sake in his hand at all times.
Tanjirou does his best to make him smile, he introduces him to his sister and realizes with relief that the boy is not afraid of her. They get along quite well.
One day, he finds him in the kitchen, trying to make dinner for everyone so Tanjirou volunteers to help him. Even though Senjuro insists he's a guest and shouldn't be helping with those things, he agrees eventually.
"Senjuro..."
"Yes, Tanjirou-san?"
"Will it be okay if I hug you?"
The beta boy freezes and Tanjirou fears that he just crossed an invisible line he shouldn't have crossed, but then, with tears in his eyes, the pup nods and jumps into Tanjirou's welcoming arms.
"You remind me of my mom," he confesses in a whisper, burying his face in Tanjirou's chest.
"Was she an omega too?"
"Yes... But it's not that... It's just... She was kind too," Senjuro stammers before bursting into tears. Tanjirou lets him cry in his arms, stroking his back and kissing the top of his head every now and then until he falls asleep.
Kyojuro finds them like that; the sweet smell increases suddenly as he stares into Tanjirou's eyes.
"Could you please take him to his room while I make dinner, Kyojuro-san?"
With a slight blush spreading over his cheeks, the alpha nods before carrying Senjuro in his arms.
"You don't have to do this, Tanjirou..." It's weird to see Kyojuro so flustered, the omega doesn't know why he's acting like that.
"I want to."
He's carefully chopping the onions when another alpha walks into the kitchen.
"Senjuro is not your pup."
"I know," Tanjirou mumbles, looking back at Shinjuro. "But I still want to take care of him."
The older alpha mumbles something about Ruka before taking a step closer to the omega, when Kyojuro comes back and jumps in the middle of the two, with his back on Tanjirou, hiding him protectively.
The omega can't see what expression the young alpha is making, but he knows it must be one filled with anger, because his scent is getting stronger, almost overwhelming.
"This is the one then..." Shinjuro comments, looking back at his son with surprise. This time, he leaves the bottle on the floor instead of taking a sip like he usually does.
"We were just talking, Kyojuro-san," Tanjirou tries to calm the alpha down. "I'm alright."
Shinjuro looks from Tanjirou to Kyojuro and takes a step back.
"I can see why... He's a good one," he blurts out, surprising Tanjirou. "A good omega. Your brother adores him already."
When he walks outside and leaves the bottle behind, Tanjirou finally relaxes completely.
"Are you alright?" Kyojuro asks him, turning around quickly.
"Yes, I'm fine."
"Would you like me to help you?"
"Yes, but only if you do as I say," Tanjirou mumbles, trying to hide his amusement. "Because Senjuro has told me you're a terrible cook, Kyojuro-san."
"I'm afraid he's right," the alpha nods, bursting into laughter. Tanjirou likes the sound of it.
Turns out they make a good team in the kitchen after all.
***
After finishing the training session for the day, Kyojuro sits next to Tanjirou outside and watches in silence as the omega thanks Senjuro for the clean shirt by running his fingers through his hair.
"You're good with pups," the alpha comments after a couple of seconds of silence. Senjuro has gone back inside so Tanjirou is alone with Kyojuro again.
"I like them."
It's the second time Tanjirou notices the alpha getting flustered and wonders if there's something wrong.
"Would you like to have your own someday?" Kyojuro asks, looking at Tanjirou almost shyly.
"Of course!" The omega beams, he enjoys talking about that so much, he doesn't pay too much attention to Kyojuro's red cheeks. "I want to have five, no... Six, at least!"
It seems like his answer pleases Kyojuro, because the alpha's eyes glimmer like they're on fire for a moment.
"I know you'll be a good mother," Kyojuro mumbles absentmindedly, like he's talking to himself. "You'll look even more beautiful pregnant."
When Tanjirou's face turns red, Kyojuro seems to realize what he just said and tries to apologize immediately.
"I'm sorry, my boy! I shouldn't have said something like–"
"It's okay," Tanjirou assures him, he knows his cheeks are still pink, but he feels less flustered now. "I... Thank you."
After a couples of seconds of silence, Tanjirou decides to go back inside to take a bath. He rises and starts walking away, but stops the moment he feels a strong hand around his wrist, as he turns around he gets surprised when he notices that Kyojuro is kneeling in front of him.
The look on his face is soft and full of... love.
"I... I want to be your alpha," he smiles, taking both of Tanjirou's hands in his. "I'd be honored to be your alpha."
"Really?" The omega doesn't quite believe it at first; he's a hashira, the flame hashira... And Tanjirou is just... Tanjirou. "But..."
"Only if you want to. I understand that you... I mean, you can choose whomever you want and there are probably better alphas than me, but if you give me a chance..."
"What do you mean better alphas? And when you say that I can choose whomever I want–"
"Well... You're perfect, of course you can have anyone."
Tanjirou is speechless. He realizes in a second that Kyojuro is being completely honest; he truly believes Tanjirou is perfect. He can't even tell him that there's no alpha better than him because he can't utter a single word at the moment. Tears start falling from his eyes.
"I'm sorry, Tanjirou! I didn't mean to–"
The omega shuts him up with a kiss.
"I think you're perfect too."
"Does this mean I can be your alpha?"
"Yes!" Tanjirou nods. He chuckles as Kyojuro takes him in his arms and starts kissing him all over the face.
They walk inside holding hands and when Senjuro notices, he puts his arms around Tanjirou's middle and welcomes him to the family.
"I want to be there when you tell Nezuko, Tanjirou!" The little boy says excitedly.
"Of course," the omega grin fondly, ruffling his hair as he feels Kyojuro's lips pressing against the back of his neck; it already feels so natural, Tanjirou is sure they'll be good for each other.