Were there any other abilities you considered giving Yuumi, that while fitting the character just didn't fit her kit at all? I figured maybe something with portals might have been considered given Book's story.
Also, I love Yuumi a lot. I know she's getting a bit of a bad rep right now, but I do fully believe it is due to the fact that a lot of players suddenly became support mains with the new champion. So because she isn't a killing spree kind of support like Pyke was, people are saying she is weak. As a support main who plays a lot of healing champs like Nami, Soraka, and Taric, I think she is a wonderfully fun champion who can be extremely powerful in the right hands, and the right comp. ♥
We actually tried a spell where she would do a mini-ryze ult to teleport anyone in a circle around her to the targeted position. It was way too much safety granted to her ally, who if ever CC'd would just be whisked away, but it was a cool portal call out.