I think Yui would make a perfect Kindergarten teacher. She's not really teaching them anything besides having fun and playing around, she knows how to play musical instruments (and has perfect pitch no less!), she's got a myriad of other quirks that entertain kids (like she is mentally). It is a perfect fit.

Two things bothered me about this episode. The biggest was that Ui wants to follow Yui to keep her out of trouble. Sure, she is the perfect little sister and more of a mother to the Yui than their wayward parents are, but she needs to live her own life and not be held back by her sister. If Yui wasn't so oblivious, she'd probably wish for the same thing.

The second was young Mio. The shyness was cute when the two were really young, but she was pretty obnoxious about not wanting to read her essay. It really detracted from the earlier parts.