MP+ is a recurring ability in the Final Fantasy series. It is a support ability that increases a party member's MP. Usually the boost is a set percentage of the character's base MP, though not always.
The Bard's Hat increases the equipped party member's max MP by 12.5%, while the Minerva Bustier increases it by 25%. Crystal Orb relic raises max MP by 50%. Phantom has MP+10% as a level up bonus while Fenrir has MP+30%, increasing the MP the user gains when they level up while equipped with their Magicite.
Materia can be granted MP+ as a support ability through Materia Fusion. The potency of the boost ranges from 10% to 999%.
MP +10%, 20%, +40%, +60%, and +100% can be accessed by equipping various accessories. MP +10% can be accessed via equipping Black Ring, Arcane Tome, Black Tome, and White Tome, MP +20% by equipping Heady Perfume and Wizard Bracelet, MP +40% by equipping Silver Bracer, MP +60% by equipping Gold Bracer, and MP +100% by equipping Rune Bracer, Iron Duke, Minerva's Plate, and Key to Success.
MP+% is a bonus on various food and equipment, though food tends to have a soft cap. Summoners and Scholars (and Blue Mages, with the right spells set) have the Max MP bonus trait, granting them a bonus of +10 MP per rank.
MP Boost increases the user's Max MP depending on the level of the MP Boost ability, while MP Grow increases the amount of MP the user gains upon leveling up, once again depending on the level of MP Grow. MP Boost can be customized onto equipment from Spirit Stones, while MP Grow can be customized through Small Morion and Morion.
MP 10% Up is learned by Freelancers at job level 7 (requires 1 slot to equip).
MP 20% Up is learned by Red Mages at job level 2 (requires 2 slots to equip).
MP 30% Up is learned by Conjurers at job level 12 (requires 3 slots to equip).
MP +20% is the level 5 ability of the Summoner class, requiring 130 AP to learn. It requires 1 slot in order to equip and use.