Manifest grants Tamaki the ability to enhance his limbs with the characteristics of anything he consumes.
Tamaki can manifest certain traits of any food he's eaten while it's still active within his digestive system. For example, if he eats Takoyaki, he can transform his fingers into octopus tentacles and if he eats a clam, he can harden his hands into a clam shell, etc. Multiple simultaneous manifestations of different foods are also possible.
Manifestation occurs only on command and any trait can be dismissed at will.
The transformation is maintained by the amount of the respective item within Tamaki's system. If Tamaki's system were to run low, this would render him unable to manifest any characteristics. He must replenish his arsenal by eating certain foods every single day.
Tamaki has mastered his Quirk through vigorous training. He possesses the ability to manipulate feature selection, size manipulation, and simultaneous manifestations. This gives Tamaki's fighting style incredible variation and unpredictability.
Tamaki makes sure to eat plenty of Takoyaki and clams every day because they're useful for both offense and defense; he often uses tentacle fingers to bind his opponents and defends himself using a clamshell husk. Tamaki has a variety of other powerful combinations as well, including using chicken talons strengthened with octopus muscles, or tentacle fingers reinforced by crab shells.
Prior to any mission, Tamaki can prepare by eating special foods for certain situations. Fat Gum fed Tamaki swordfish so that he could exploit Chronostasis' Quirk's weakness. This can also lead to Tamaki overpreparing, manifesting traits he doesn't even need to use to win.