I don't really care who expresses interest in whom, it's not a story about his harem of girls, it's not focused on his relationships and "uuoogh whom will he pick", and "harem" is most certainly not a descriptor of what the story is about, which is the purpose of tags. It's just a small thing happening from time to time. By your logic almost literally every story needs a slice of life tag because there are slice-of-lifeish events happening everywhere. Why aren't you arguing for slice of life tag here then? There have been a number of chapters not relating to the main plot in this manga.
P.S. also, out of 4, one girl peaced out probably for a very long time (Reo) and before that existed for less than a dozen of chapters, and other two only showed interest in like the last 10% or less of the story. The last one barely even features in the second half of the story.
Well… no. You're just arbitrarily introducing requirements. Most OP hero isekai have harem tags, even when the romantic part is only played for laughs. Harem is defined as a situation where a majority of female characters make advances on the male protagonist. It says nothing whether it's central, peripheral or marginal to the plot, and there's no prescription on percentages. Whatever exposition time these women have, they're fawning on him. That's all it takes. Sexual violence is a tag and happens about 10% of the pages, too. You could argue that sexual violence is a trigger tag, that people choose not to read a series if it's present, and as such even if it's just one incident, it should be added. Well… harem is a trigger tag for some people too, and I'm pretty sure they'd be equally irked by the events here as if they happened more often.
SoL I agree with you is an abused tag. In principle, I think it should only apply to characters who're living ordinary lives that could be lived by real people. You see the SoL tag even in fantasy series, which is plainly absurd. But that's not the hill I wanna die on. This is not a SoL because nobody here is living an ordinary life. Full stop.
This is a harem. It's a thriller, revenge porn, sexual violence, tragedy… and a harem, too. The author seems to be writing straight from the loony bin. It's so bad it's hilarious, which is why I'm still reading it. And having harem scenes alternating with revenge porn makes it
more hilarious. Live with it.