ushiten and #6 for the otp ask game thingy!!
OOOH I had to think a lot about this, you're such a brain cell stirrer
#6: what's their favourite feature of their partner's?
To me, Ushiten is about accepting each other's weirdness and loving the other for it. What draws them to each other is what makes them stand out, for instance Ushijima is always drawn to Tendou's energy, which is something he was bullied for the in the past.
SO, Ushijima probably really likes Tendou's hair. Y'know, it's a little odd compared to everyone else in the world, but it's what makes Tendou Tendou. Ushijima definitely seems like a Hair Player to me, even when Tendou cuts his hair off. Eyes were also shortlisted for this, since they reveal Tendou's true personality at all times; even when he's trying to be quiet, they're always full of energy.
I was tempted to put "Tendou loves Ushijima's blank expression" but maybe that doesn't count, so probably eyes for him too. Ushijima always looks really stubborn and solid and neutral and boring, but Tendou knows how to read his eyes & expression. Tendou can see the little spark when Ushijima makes an awful joke, or the fire when his team is losing and he's about to turn the tables.