I Died 999,999 Times: Unlimited Level-up With My Immortality Skill

A brief description of the manga I Died 999,999 Times: Unlimited Level-up With My Immortality Skill:
White Lotus, the world’s strongest hunter guild, is praised as a group of heroes for defeating the Demon Lords.
But their power comes from something far darker—ruthless and inhumane cruelty. They captured Makoto and Minori, a pair of immortal siblings, and slaughtered them repeatedly to farm experience points.
Desperate to survive and fueled by vengeance, the siblings make a brutal choice: killing each other to level up.
“Let’s begin our revenge.”
Through relentless battles and newfound powers, they carve a path of blood and retribution.