A suggestion

Well, I haven't seen this in the game yet and it's my favorite zanpakutou, so ...


Hirako Shinji's Zanpakuto!

Now, what I was thinking was that it would be attack based, and what it's shikai would do is invert the controls of your enemy. This would drain your Rei for the duration, and you would have the option to turn it off. This means, since it would drain even when mastered (when mastered drains less), that it should have a decent amount of boost, something like Aizen's.

Then, for bankai, you could perhaps have a setting, and it would ask you one by one what you want to set the opponent's movements to.
Example: You click the verb, a popup shows up "Where do you want your opponent to move when they press the left arrow?" and four choices show up [Left, Right, Up, Down]. You choose this for each of the movements, and then it's set. Depending on whether it would be op or not you can make this unchangeable once it's set, or just let people change it up.

Other possible abilities could be thought about, but for now it's about the stuff above and if it's even going to be implemented.

Edit: Bankai's ability should drain the same amount as Shikai's, or maybe less. W/E is acceptable.

Nice idea, but i think the drain of the bankai would have to be higher than shikai since you would can choose the settings.

The problem are the npcs, since them dmg are most meele, this would can be a op zan cause they barely would can hit you.

What would be your solution about the npc balance?

Greetings

Well, against npcs....there's only one thing to do.
Have it not work on them, similiar to Aizen's illusion techniques. But the attack boost would have to be as high as Aizen's, to not make it useless against npcs.
Although if Shinji had more abilities than just the reverse world, it might be balanced to not have it work against npcs.

Then theres no problem with your suggestion, hopefully critic make this new zan cause it would be funny