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I feel like Kirishima uncle has to do with Yoshino father's death. Probably there is more to it that's why they needed to protect Yoshino. And Kirishima dude that's obsession right there ya know? The way he expresses his love is way over the top. I remember the part where Yoshino ask him what will he do if she cheated on him and his answer is not something you would expect. His main objective is to protect Yoshino and Yoshino alone. Other people don't matter even himself.
Theory take it with a grain of salt