Perhaps if you were sat in front of someone dear to you then you'd return human. The Corps were taking chances of seeing if maybe they could find the cure for demons. It took a lot of convincing but Sanemi finally set off to face his old friend now turned demon

You were tied up into ropes in front of Sanemi, you weren't fighting. The Kakushi's said the only thing you'd do is ask if your lord was okay

"This is pointless. What do I do? Their mind is far gone already."