This article's content is accurate to the most recent public game version, 0.4.8d.
"Alice reduces her HP by 15 to restore 30 MP."
Cost: 15 HP
Source: Alice - Starting skill.
Inner Reserves is a skill that restores 30 MP at a cost of 15 HP.
As 15 HP isn't a lot (and 30 MP is one and a half times the cost of the powerful Doll Girl's Anger), it is more than fair trade. Just be sure to be careful with using it.