Drain is an indirect magic spell in Final Fantasy VIII. The spell steals HP from the enemy and heals the spellcaster, though this is reversed if the target is under the Zombie status or is undead. Drain can also be junctioned to boost stats, and notably, can be junctioned to ST-Atk-J to cause all physical attacks to heal the user slightly.
Drain is similar to the command ability Absorb.
Drain is a rare spell only drawn from a few enemies. It can be refined from Vampire Fangs using the Guardian Force Leviathan's ability Supt Mag-RF. This makes fighting Red Bats (and their cards) and Glacial Eyes a good way to obtain Drains, as they are a good source of Vampire Fangs.
Drain steals HP from the target and returns it to the caster. It is cast using the Magic command, Selphie's Slot Limit Break, or Rinoa's Angel Wing. Casting Drain in battle doesn't affect compatibility with Guardian Forces, and is one few spells at that.
The Guardian Force Pandemona teaches Absorb, a command ability that has a similar effect to Drain. This makes Drain mostly redundant when cast as a spell, as it is better instead to junction it.
Drain when junctioned provides moderate boost to stats, but more importantly, can be junctioned to ST-Atk-J or ST-Def-J to either render a character immune to Drain, or to apply the Drain status effect to all physical attacks. This means that all physical attacks will heal the wielder, and renders Drain a solid choice for ST-Atk-J against non-undead enemies.