Ultraspeed Regeneration

Ultraspeed Regeneration (超速再生) is an Extra Skill that is the enhanced version of Self-Regeneration.

Rimuru had obtained the skill after his Unique Skill Great Sage combined his slime-specific Intrinsic Skills Absorb, Dissolve, and Self-Regeneration together with the Mimicry of his Predator using his recently acquired Degenerate. Shion had also obtained it as an Intrinsic Skill after her revival following the invasion of Falmuth.

Effects
As can be guessed by its name, it grants the user incredible regeneration properties far superior to Self-Regeneration. It's considered equal or better than the Orc Disaster's regeneration combination of Starved + Self-Regeneration, which was implied to require the destruction of the entire body on an atomic level to beat.

However, the regeneration is blocked when a wound has been caused by Spiritrons, for example via Disintegration. Also, damage done to the Spiritual Body can just bypass the regeneration itself altogether.