You have to buy them during nightime at the love hotel, but be careful, because you have to buy the right size, wich depends on your boyfriend. I dont remember the name of the sizes but from left to right, it is :
Toru-chi > Hikaru > Tocchan > Shuu > Shiba
Once you bought a good costume with the right size, you can use it during foreplay mode ^^
Thanks for the answer! But I think I didn't structured the question the right way. What I wanted to ask was how Hatto wore the costumes himself, because on Meyaoi's patreon there's a photo of Hatto with the cat costume! But I've already found out (at least on Shuu's route): you have to wait until it's his birthday and he'll ask you to wear it as a birthday present (I made Shuu be dom top, but I don't know if that really matters)
