Yuffie and Cait Sith attack in tandem with a secret ninja technique.Description
Moogle Pinwheel is a synergy ability in Final Fantasy VII Rebirth, used by Yuffie Kisaragi with Cait Sith as a synergy partner. It costs three synergy charges each, performs magic damage to a target, and grants them temporarily unlimited MP for a duration.
In the ability's animation, Yuffie and Cait Sith pose to charge their energy, then summon Cait Sith's moogle. Yuffie then hurls the moogle forward at the target, sending it along with a tornado.
Obtained
Moogle Pinwheel is unlocked on Yuffie's folio, and costs 20 SP.
Use
Moogle Pinwheel costs three synergy charges each on first use, and four on subsequent uses, and will grant Yuffie and Cait Sith unlimited MP for a duration. This allows them to freely use spells, limited only by ATB charges and not by their MP, and by the spells they have in their equipped 
Magic Materia. Yuffie has balanced attributes giving her strong 
Magic Attack, while Cait Sith has one of the stronger magic attack attributes in the game. Yuffie's Doppelgänger also makes her a very strong potential spellcaster.
Both Yuffie and Cait Sith have another synergy ability, each with Aerith Gainsborough, that can grant unlimited MP. Yuffie with Mystic Multiplication, and Cait Sith with Kitty Cannonade.
Yuffie's Doppelgänger, when deployed, will cause her spells to be cast twice (or even four times from an Arcane Ward), albeit the second time at reduced damage. This, and her ability to build ATB quickly, makes her a strong potential spellcaster, and giving her unlimited MP can unlock this potential further. Cait Sith can also be used as a very strong spellcaster, meaning both of them can benefit greatly. However, the usefulness will entirely depend on their equipped materia.
In Hard Mode, gaining unlimited MP can be more crucial as means to restore MP are more limited. The player may also have the rare and expensive 
Reraise spell available, perfect to be cast during any MP-free period. Any 
MP Absorption Materia effects will also restore MP even if the casting was free.
Etymology
A pinwheel is a simple toy made of a wheel of paper or plastic curls attached at its axle to a stick by a pin. It is designed to spin when blown upon. Pinwheel is also a type of traditional Japanese origami form that can be used as a toy pinwheel, as a base for more complicated models, or as a component of modular origami. In Japanese culture, the pinwheel can represent the cycle of life and becoming a child again, the turning of the pinwheel representing the Buddhist teaching of reincarnation.