Yeah, it should probably have a lolicon tag regardless. Yuka is described as being a "middle school" student, but that's probably just because of the split between school grade designations between the US and Japan. (I don't know which country the English translators hail from, so I can only speak from my own viewpoint.) The US typically has four breakdowns of the different "grade school" levels: elementary, middle, junior high, and high, which roughly corresponds to grades 1-5, 6-7, 8-9, and 10-12 respectively. In Japanese it's 小学生 ("shougakusei"), 中学生 ("chuugakusei"), and 高校生 ("koukousei"), which generally corresponds and translates to "elementary school" (years/grades 1-6), "junior high school" (years/grades 7-9), and "high school" (years/grades 10-12). Given that Yuka is likely a "chuugakusei", she's probably year/grade 7-9, which would mean she's between 12 and 15 years old. Even if 15 is possibly beyond the limits of what is technically "loli", she's drawn in such a fashion that she definitely looks young. (Granted, she doesn't look that much younger than any of the other girls, but I'll chalk that up to the art style, since they all look kinda young, even the OL.)
Yeah, that's not great for Masato, who's established as being a first year college student, likely aged 18 or 19. If Yuka is in grade/year 9, then that's the best scenario, but that still pits her at 14-15 versus Masato's 18-19. (And honestly, the older she is, the more believable it is that she can overpower him, even assuming physical differences in this alternate universe.) Regardless of how understandable it would be for her to pursue him romantically, it's still disturbing for us the readers from an age and power standpoint. And that's not even addressing the probable fact that Masato honestly doesn't have as much agency as he believes he does, being on the wrong side of the gender ratio, not to mention the physical ratio.
So yeah, Yuka is awakening as a very aggressive junior high student who can physically take advantage of a college-aged man, and that's an extremely disturbing thought if you're that man. Consider if you befriended five girls, and the youngest of the five was able to physically overpower you. And now they're all showing similar signs of attraction. Yeah, that's some significant levels of horror, that you laid groundwork for all five of these girls to become hopelessly attracted to you, and there's nothing you can do about it, physically or economically. You are about to be dominated, and it's the youngest that tipped you off first.
also she basically forced him, he's the victim
