The scenario is this:

A couple months after the defeat of Ywach spiritual activity in Karakura town remains abnormally high so rather then communating between realms Riruka accepts a long assignment in the living world.

Yet due limited house arrangements she is now stuck with you. Basically the premise of it.

Users Bankai (sorry if u don't like): Chishio which means crimson tide or flowing blood.

The premise is simple. Your Zanpakuto is like Choso from JJk. You control blood and your sealed form is a Katana with a crimson edge to it.