Just an idea.

This is going to be mostly about Shinigami, but if someone else wants to add anything, they can. This isn't a complaint, but just an idea to improve some shinigami characters, or just add another layer.

The racial skills, there isn't anything for reiryoku, or reietsu control. We've seen in the show, and manga that these are important factors to some degree. Like when Yoruichi, or soi fon use Shunko, and this requires mastery in a multitude of things.

Reiryoku itself supplements the usage of all shinigami arts such as Hadō, their Zanpakutō techs, etc. Giving this a rank would literally give people their finite reserves, and an idea of how to gauge it. Also, like any other technique, you can improve your reserves.

Reiatsu, when exerted, can have adverse effects like freezing the area around them (shown by Rukia, and Toshiro) or fire everywhere like with Yamato. Giving this a rank could allow people to create their own effects. The two would normally be worked on together, or only ever go up with tier, and sub-tier rank ups.

This is all just wild speculation, and ideas while I was doing my training threads.

Bump-le-bump