So it's a prologue so there isn't a lot of feedback I can give, given the length of it. The premise is straight forward, it's an like an isekai but not in the traditional format as the MC and sister are both alive, but in another realm so I like the unique take on it. I didn't notice any grammatical errors on the first run, the renders are nice, there wasn't any choices so who knows how impactful decision making will be, and the realm you go too looks interesting along with the mystery around the sister.
As for the cons, the major one is how the MC looks, I get he is a fighter, but all the veins makes him look roided out and weird, and the face needs work. I can't take the roided man with what looks like lip filters seriously, at all. Also knowing what the planned tags are would be nice to know, I assume harem given whats in the spoiler