I found a belt in the Honkai Impact 3rd world.

"To deal with the Honkai, we really need the power of the Valkyries. (Shows a card)"
"Isn't it because you don't have a Knight Card? Forget it, you're brain-dead! Go ahead and attack!"
You're the one with cerebral palsy!
In short, it's a delightful journey for the foul-mouthed belt and the protagonist.
The cover is unrelated to the content (probably), there is no moe-fication plot (confirmed), there is a brief transformation (fighting as a Valkyrie) plot (note), it is a newbie work (seriously), that's all.