In terms of character introduction, the new girl feels a little bit too forced even if she was meant to create his training arc
Hanako could've just told her backstory to him in a lot of future scenarios I'm stirring up in my head (which includes rain scenarios, trapped in a room cliches, so on and so forth)
I do agree the new girl feels more out of place than the rest of the cast. If she was cleverly hidden/drawn in the previous chapters stalking him in the background then I would've respected her and the author/artist much more because of that detail (I myself haven't really checked, so I don't know for sure)