Welp, Eien might be fucked. He is unarmed, and he is forced to fight some guy who could easily defeat someone while being malnourished. Theres no way he can win unless he manages to pull off a reversal on the boy through two means.

1. Do what he did to the girl, and force him to stab himself in the stomach.

2. Lure him up stairs and force trick him into falling into the abyss.

I feel like the latter scenario might be better xD