Shigeo's attitude,Haru's utter distrust towards him and some uncanny resemblance to Souta in his facial expressions AND speech patterns raised some ominous red flags to me (i had to reread the raw version too bc of said flags being a bit diluted in the translation, and my initial fear was true, as stepdad uses "boku" as a 1st person pronoun despite of behaving more like an "ore" user. Who's the only character who uses "boku" in this manga? Souta ofc).
Chances of Haru's stepdad being Souta's biological dad and a sexual highschool girls' predator have increased a lot after chapter 19