When Tatsuya was young, his brother marked each birthday with a different kind of cake. One year his brother made Taiyaki to share with friends. Katsuya is pretty experimental with flavors, and some are better than others. Tatsuya doesn't have a lot of friends, so he shared it with Anna and the track team after practice that day.
Schools start in the later half of July in Sumuru, and the track team practices outdoors only on the cooler days, the other days passed in the shitty air conditioning of the gym. Everyone eagerly awaits September, where the days will get cooler, and dread November where the days get too cool for easy practice. Summer break is instead a long spring break, apparently in keeping with the ancient traditions of the Nobles who once lived here. It's hard to plan things with people who live in other cities who get regular summer breaks, but apparently Sumuru stands by their ancient Nobel traditions, and Tatsuya is in no position to argue with the ancient traditions of the dead.
The team calls Tatsuya an honorary member for sharing, and it's easy to make a tradition.
Even when his relationship with Katsuya is no longer easy, there's still cake in the fridge. Plain chocolate in the harder years, but gradually they become more elaborate again.
One year, Katsuya invites Anna, the track team, and his weird friends, and throws him a surprise party in August. There are a lot of variants of Imagawayaki.
Tatsuya is certainly surprised, because he has already had his birthday.
He is even more surprised when more people show up. Lisa (who has a crush on him), and two guys from their rival high school. He's never met them , although they claim they have met him. The cute guy even claims Tatsuya once pushed him off a blimp (what!) And saved his life.
Katsuya explains that Tatsuya probably suppressed that memory from trauma.
Jun claims he wishes he could, and mutters something about pushing someone off a top story floor.
Tatsuya decides he really does not want to know, and would rather get to know him outside of that context.
His brother asks to talk in private after the party. It turns out to be a long one, with apologies and explanations on both sides. They're not completely at peace after it, but more at peace then they were before.
On the other side, as they called it, Tatsuya feels he should probably make some amount of peace with Katsuya. Their relationship going south is both of their faults, and a lot of their family bullshit.
So he waits until December and Makes Katsuya a honey Castella. It's something that's supposed to be easy, and he messes it up anyways. Regardless they both eat it, and while it took them until after the end of the world to start repairing their relationship again, it's a good start. They both laugh about that when he brings that up, and while it's kind of awful, in a way it's healing too.
I love that Katsuya wants to be a patisserie. I imagine he was quite experimental in his flavouring choices, and Tatsuya tried so many variants