I predicted it, i fucking predicted it lads. The kabaneri girl faced the consequences of charging in like an idiot and was crushed by a fucking boulder. She starts going all emotional because she wants to live but she doesn't want help from the lad she is starting to fall for. In the end he helps her, there is some boring dialogue about friendship and together they get out and defeat the big bad monster with the power of friendship.
Mumei never confessed and saying she developed romantic interests towards him is a bit of a stretch based off this episode alone.
She hasn't confessed, but a romantic or a sibling type relationship is developing slowly. He'll be the one to protect her, feed her and be by her side etc. Give it some time and she'll fall in love with him. Her brother seems a bit annoying though. Also, what's that annoying discarded old guy doing with those lowlives, plotting some shit? I'd like to see what happens in the next episode