Responses
I've read many comments theorizing that Yoshino's drastic design change is because of a change of POV but it's simply the art style change, it's most striking with Yoshino. But compare how Kirishima looked in chapter 1 vs how he looks in chapter 37. It's a art style change, not a POV change and it doesn't apply just to Yoshino's design.
Her looks have always been a point of discussion in manga, but the Mangaka is suddenly making her look... softer? Or is it a changing POV? It could be that the earlier version was how Yoshino saw herself, and the current look is how Kirishima and others view her. I love the Mangaka's art-style, so I hope it's something like that, instead of them trying to change their style to make their female characters meet conventional beauty standards more.