Oshimaida arise when individuals emit overwhelming negative energy called Prickly Powerer, which spreads and coalesces into an entity embodying the collective negativity. Created by the Criasu Corporation's employees, their forms manifest wildly diverse appearances, frequently influenced by objects they possess or the victims whose Prickly Powerer fuels them. Documented forms include clocks, cranes, balloons, flowerpots, computers, traffic signals, and human figures such as Umehashi-sensei or Yoshimi Rita. All standard Oshimaida wear company ID badges around their necks. Upon purification, they declare "Yamesasete moraimasu".

A more powerful variant, the Mou-Oshimaida, emerged after George Kurai's resurgence in episode 23. Typically summoned directly by Criasu agents like Gelos, Bicine, or Doctor Traum, Mou-Oshimaida may lack ID badges. Without a human host, they can rampage uncontrollably. Their abilities are often significantly more destructive; examples include a skeleton Mou-Oshimaida launching fireballs and an hourglass Mou-Oshimaida generating tornados. Their purification phrase is "Mou yamesasete moraimasu".

Specific Oshimaida demonstrate unique abilities tied to their origin. A florist's despair formed a carnivorous plant Oshimaida capable of extending vine-like arms. A computer-based Oshimaida utilized combat data analysis to evade attacks. Mou-Oshimaida summoned from emotional turmoil, like Emiru's grandfather's frustration over family disobedience, manifested as a palace with octopus-like tentacles. In episode 29, a bike delivery man's irritation after being scolded produced a candy-themed Mou-Oshimaida that threw candy-shaped projectiles.

The Pretty Cures consistently defeat Oshimaida through purification techniques like "Heart For You!" or "Trinity Concert", cleansing the Prickly Powerer and returning victims to normalcy. After purification, affected individuals resume their lives, such as Umehashi-sensei supporting Homare's skating or Sakita Mari regaining her passion for floristry.