Yui Kodai

Yui Kodai, also known as Rule (ルール), is a student in Class 1-B at U.A. High School, training to become a Pro Hero.

Appearance
Yui is a young girl with shoulder-length, bob-shaped hair, sideswept to her right with some shorter strands hanging above her eyes. She has fair skin, an athletic build, cerulean eyes, and she's usually seen wearing a neutral expression on her face.

Her hero costume consists of a simple red bodysuit with a white collar trim, a matching ”V” pattern running over her chest and around her upper arms, which also includes a short white skirt with a red design at the front, dipping so it follows the one in her chest. She wears plain vambraces, as well as a hat which resembles the front of a baseball cap, colored red with white U-shaped lines around the sides, with a metal piece resembling a fin attached at the back of the strap around her head. She has a belt at her waist and straps around her shoulders, what appears to be an oval-shaped gemstone set between them on her chest, each adorned with a small pouch, containing the various nuts, bolts and all of the other small metal pieces she likes to use with her Quirk.

Personality
Yui is a quiet girl that rarely expresses any emotions; some of her classmates even consider her a kuudere. Despite her silent demeanor, Yui has shown to care for her classmates, notably during the Forest Training Camp Arc, when she looks after her classmates, Juzo Honenuki and Ibara Shiozaki, after they get knocked unconscious by Mustard's poisonous gas.

Quirk and Abilities
Size (サイズ): Yui has the ability to alter the size of objects that she interacts with. Its function appears to be similar to that of Ochaco Uraraka’s Zero Gravity Quirk, as Yui can only activate this power by pressing five of her fingertips together. However, her Quirk doesn't work on living things.

Trivia

 * Her name contains the kanji for "small" (小), "big" (大) and "ordinary" (唯).
 * Yui's rankings on the Popularity Polls are as following:
 * Ranked 118th place in the 4th Popularity Poll.
 * The crest on Yui's hat of her Hero Costume resembles 's . Ultraseven was known for changing in size, much like Yui's Quirk.
 * Volume 22 mentions that Yui was unaware that a group of boys formed a fanclub for her during her middle school years, even when she graduated at some point.
 * Yui also appears to like matryoshka dolls.