The Tower's Regressor is a Coward - Reincarnated as the Villain

What should you do when you transmigrate into a hit tower-fantasy novel? That's right, you should find and bite on the skin of the overpowered character who will keep you alive even if you die. Not necessarily the protagonist or the antagonist, but that very one you're thinking of. The cold-hearted, aloof, overpowered character called a regressor. Yup. You should cling to that character. Then why? Why is this damn regressor such a coward?