A little bit about leveling up:
Shira and armor have their own level.
Shira is leveled up if she defeats monsters, in fact, there is no point in leveling her up, since it just unlocks new combat skills and stats, I think even the initial level 30 is enough to complete the entire game right up to the last boss.
With the pumping of armor, everything is more interesting, the experience gained is equal to the pleasure inflicted. This damage can be accelerated quite a lot if you increase the sensitivity of a certain part of the body, and use armor skills .
With each new level, a new skill opens up, allowing you to control the battle process.
The last 2 skills open at level 56 and 80, so it makes no sense to upgrade armor above LVL 56.