Osmose Blade (アスピル剣, Asupiru Ken?, lit. Aspir Sword), also known as Osmose Sword, Syphon, Aspir, Osmotic Slash, or simply Osmose or Psych, is a recurring ability in the series. It allows the user to drain the target's MP without damaging them and usually requires the Osmose spell in order to use it.
Osmose is a level 6 Spellblade ability that costs 15 MP to cast.
Osmose Blade is a rank 3 Command Materia that costs 2 AP to use. It can be obtained as a reward for completing Mission 5-2-6. Another version called Power Osmose exists as a rank 6 Command Materia that costs 6 AP to use, and deals significantly more damage than Osmose Blade. Power Osmose can only be obtained through Materia Fusion.
Aspir is a level 4 Sword Magic spell. It imbues a weapon with an MP absorb effect for ten turns. Attacks with this weapon will absorb MP from the target. It costs 1 MP to use. It can be bought in Starkfort for 1600 pg.
Osmotic Slash is an ability of the Magic Sword skillset, usable by the Red Mage class. It costs 10 MP to use.
Osmosis is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves across a semipermeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations.