Yes, our MC helps Tojoin during this date and saves her from becoming a losing heroine. As far as I read the WN, it didn't become a harem yet. I don't know about the LN, sorry.
That's why I respect the author of "We can't study" alot. Man literally made multiple ending for each heroine so that everyone can have a happy ending.
I have a way of distinguishing them. Hisamura (our MC) has a bang covering his forehead while Shigemoto (in-universe MC) has a split bang in the middle. I think he also has a mole near his eye.
Whole premise wouldn't make sense if it becomes a Harem anyway. He strictly said even when he was still in the old world, he was heavyly simping for Sei. If the title was "saving the losing heroines" now that would be a different story.
such is life
Short answer: No, don't worry, the only losing heroine intended is Sei.
IMHO, the Mashiroiro did a very good job of presenting the reality of how a harem with competing tsunderes would actually fare: instead of going for the prickly girls that insult him and assault him, the MC went for the natural choice of going after the one girl (other than his sister) who actually treated him nicely and made him feel like she cared about him; the girls being heartbroken also showed the sad reality that many mangas and animes never show: the poor girls were frail teenagers who just got their hearts broken, so of course they're gonna feel miserable about it, not to mention that it was because of their own actions, so they actually faced the consequences of such behaviour.
Well there is no harem in this, you could say that his actions later on could possibly spawn some feelings towards him fron the other girls, but as it stands ain't nothing getting in the way of sei-chan and hisamura, he ain't even looking at anyone else and neither is she.
