Ok, I went and read through all the aggregated trash (god isekai scans suck) TLDR; The other little douchebag is a hero or something adjacent, they need to escort the little girl, lotta zombies killed all other adventurerer on the quest.
So, after he tried to grab the longsword the little twat got mad at him, but oh hey there's an even BETTER sword that he got. So, he and a bunch of other adventurerer were assigned a quest to help transport a little girl to a city, and the twat complains about how mc isn't high enough rank, it's all nepotism from silver ranks. While on the way, the wagon with little girl on it had everyone get ill, poisoned by magic. They burn the bodies, everyone gets a little sus of the girl, but they keep going. Then they get attacked by revenants, and it turns out the twat is probably a hero or something like that. They pack up, and in the night run into a massive horde of undead. The carriage drivers took the horses and fled, and then everyone but mc party and the twat party have died. Big skeleton dragon picked up one of the girls from twat party, then fmc casts holy magic and mc hits it with a sword. Aaaand now this chapter starts.