Nasak is an advanced sacrificial healing technique common to Phantasy Star games.
Phantasy Star series
Phantasy Star II
In Phantasy Star II, nasak costs 1 TP to cast. It fully restores the health of all party members at the cost of the user's life.
Amy and Nei are the only characters that can learn nasak in the game. Amy learns nasak at level 12, and Nei learns it at level 24.
Phantasy Star III
In Phantasy Star III: Generations of Doom, nasak costs 1 TP to cast. It fully heals all allies in exchange for the user's life.
Mieu, Laya, Gwyn and both possible Karas are the only playable characters in the game that are able to learn this technique throughout all generations.