So this is kinda my theory for who Maos father is and how hiriko consents to Matsu and Mao being together
Before Hiriko meets Matsu, Hiriko and her father were in a 'romantic' relationship he tells her he loves her, and she is the one for him, and then when she becomes pregnant with Mao her father reveals his true colours and freaks out demanding she get an abortion making her realise that he doesn't actually love her and he just wanted to fuck her causing a massive rift in their relationship and her to have some fatherly issues and when she discovers Mao and Matsus relationship because of her past experience ( and also obvious reasons) she is initially against it but when Mao tells her that she is deeply in love with him and he feels the same way and her not wanting her daughter to miss out on the relationship she wished she had with her father consents to them being together