I might have been able to enjoy Yui as a comic relief kind of character if I didn't keep thinking of how she was going to end up holding Ui back in life due to the Gilbert Grape kind of relationship they have going. The demands of taking care of Yui are going to ensure Ui never has a boyfriend, never advances far in her career, never has kids of her own, and all sorts of other things. Yes, yes, she loves Yui and does it willingly. That doesn't make it any less tragic in my eyes.