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Merciless (心無者(ムジヒナルモノ) Mujihinarumono, lit. ""Heartless") is a Unique Skill of Rimuru Tempest's.

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

The Skill is only able to be activated when the targets lose their will to resist. Once that condition is met, from that point on, at any time the holder wishes, the holder can reap the marked target's Soul, even if the target has recovered their will to live and fight in the meantime.

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.