Hit Points (HP) was a hidden stat in the GBA and PSP versions of Yggdra Union, but was later represented in Blaze Union and Gloria Union. In these games, each soldier including the head had HP that drained during a clash; ATK, weapon advantages, stat boosts, and elemental weaknesses were all key factors that influenced how quickly the HP of the soldiers depleted. The head's HP will not begin to drain until all other soldiers in their party have fallen. Large type units (such as Knights and Griffon Riders) have double HP in comparison to Standard (ex: Fencers and Witches) ones, therefor one large soldier is equal to two smaller ones. However, the amount of soldiers in a large unit (3 GBA/4 PSP) is half the amount of those in a small unit (6 GBA/8 PSP).
In the spin-offs, visible on-screen. This is helpful to the player, as it allows them to visually know how much more the head can take before they fall, thus allowing for better prompt decisions.