Fallen Six (Remake)

This is a what if story, it's a what if that's both scary and common in the assassins verse. What if, six first year assassins, led by Matsukaze Tenma. Have fallen in the line of battle but one of them strikes a deal to save the last of their comrades remaining life?

Now, all six of them are forcefully bound to become spirits and have to act fast to find a way to release them from their chains, trying to seeking help for their living comrades but with "haunting methods" they're forced to use due to the deal...