Merciless

Merciless (心無者) is a Unique Skill of Rimuru Tempest.

Abilities
The Skill is only able to be activated when the target's heart breaks, such as losing their will to fight or beg for mercy, etc. Once that condition is met, from that point on, at any time the user wishes, they can reap the marked target's Soul, even if the target has recovered their will to live and fight in the meantime.

History
Rimuru obtained the Skill while he was massacring the 20,000 soldiers of Falmuth's army in Tempest Holy War, allowing nobody aside from King Edmaris, Razen, and Reyhiem to live.

During the Harvest Festival, Raphael integrated this Skill with Unique Skill Gluttony which then evolved into Ultimate Skill Beelzebuth. Although the skill has been lost, its functions have been inherited by Beelzebuth.