So Fia completely forgets his dead brother and just falls in love with the MC. She's also able to participate in the contest AND able to use the parasite powers that infected her almost immediately. And it never occurs to any of them that she might not be a reliable ally. One of the party members' mind is obviously being messed with but is being camouflaged as contrived tension. And one other participant, a sword user, is missing an entire hand, but joins anyway. This suddenly smells like a wet rag tbh. Wasted so much time here, but that's just how it is here in the world of manga.
Oh, and if you want something in the same vein as this but WORLDS better, "I Left My A-Rank Party..." is a much better read. DON'T WATCH THE ANIME unless you're a literal child and want things spreaky clean. The manga is where it's at.