Borrower Hiro would have a slightly unnerving metabolism. Like, he's ALWAYS up for food, because he's SO SMALL that to keep warm he needs ALL THE FOOD. He'd probably have to go torpid at night. He spends a LOT of time snuggled up with literally ANYTHING warm, because he gets hungry really fast otherwise. Really, really, really fast. Did you know a shrew can starve to death in an hour, and a mouse in a few days? Yeah.
Thankfully he’s also teeny enough that you can hand him a cracker and he’s set for DAYS. And that’s exactly what Tadashi does, he just carries around little baggies of crackers and nuts and candies in his pockets so he can give Hiro a snack whenever he gets peckish. The others have the same habit too, but Aunt Cass is Hiro’s favourite because the snacks she carries in her pockets are her own baked goods. Mmmmm, cookie crumbs
And because Hiro gets cold at night, he ends up stealing one of Tadashi’s thickest, warmest socks and using it as a bed. On the really cold nights, Tadashi pulls out a heat lamp for Hiro and sets it up so Hiro doesn’t freeze. But overall Hiro prefers to snuggle with Mochi because Mochi will purr and lick his head and snuggle with him and the two of them keep each other warm and it’s so lovely. And unlike Tadashi, Mochi won’t accidentally roll over and almost crush Hiro in his sleep.
(It happened only once and Tadashi was so freaked out he refused to let Hiro sleep anywhere near his bed ever again. Hiro still insists he’s fine, and he was barely smooshed)