How has he not gotten her pregnant? He’s been cumming in her for over a year, it never mentioned that she’s on birth control or anything. Is Mitsuru sterile or something? Perhaps as a child she had some illness and had to get a hysterectomy, we’ve never seen her get her period or own any maxi pads or tampons and it may explain her small size even though she’s like 17.
It’s probably just hentai magic and she’s fine, but it’s odd that they’ve never even considered the possibility of her getting pregnant with how he’s constantly plapping her.