Acid Spring (酸性泉 Sanseisen) is an Acid God Slayer Magic Spell.
By channeling her magical power through the ground in an immediate vicinity of 10 metres. This creates a bright red liquid "spring" of acid which is able to corrode anything that steps onto it. It functions effectively as a defensive measure against ground based attacks, which are unable to reach her due to this. Kurenai also uses this commonly to stop large mobs of enemies.