Adult Mode (おとなモード Otona Mōdo) transformation is a shapeshifting-like magic that allows an underage caster to transform their body into an adult (or rather, late teen) form of themselves and back. The primary advantage of the Adult Mode is the apparently greater capacity of an adult body for magic channeling, compared to a child. Therefore the Adult Mode is primarily used for training, especially involving physical exercises, e.g. in Strike Arts and Kaiser Arts. It can be also used, however, to conceal the caster's identity.
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In ViVid and ViVid Strike!, a large number of young martial artists may transform into their Adult Mode of around 18 years old, but the details of their magic or spells are not explained. Notable casters among them include Einhard Stratos, Miura Rinaldi, Corona Timil, Fuka Reventon and Rinne Berlinetta.
- In StrikerS, Jail Scaglietti and Quattro forcibly transform Vivio into her "Heiliger Kaiser Mode" (聖王モード Seiō Mōdo), the original idea of her Transformation Mastery spell, by infusing her with a Relic. She is only able to revert back to her child appearance when Nanoha Takamachi destroys the Relic within her.
- It may also be seen that Caro Ru Lushe uses a spell with the inverse effect (Dragon Soul Summon) on her summoned dragon Friedrich to seal his powerful adult form, allowing him to stay with her. This is probably similar to how familiars and Unison Devices stick to small forms in order to minimize their mana expenditure.
- In ViVid, Fabia Crozelg may shapeshift into her Adult Mode when "united" with her three Petit Devils.
- In Force, Curren Hückebein displays an ability to transform into a teen-aged version of her usual self during the assault on the Rezona jail, although it is yet unclear whether she is an adult transforming back into a child, or vice versa.