I think it's because Ruri took Sui's cardigan and put it on and then he went to see sensei and sensei woke up smelling the cardigan, thats why he said Sui because he smelled the sweater.
You’re right!
I think it's because Ruri took Sui's cardigan and put it on and then he went to see sensei and sensei woke up smelling the cardigan, thats why he said Sui because he smelled the sweater.