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


Yui is a young girl with shoulder-length, bob-shaped hair, side-swept 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 a yellow 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.



Yui is a quiet girl that rarely expresses any emotions; some of her classmates even consider her a kūdere. Despite her silent demeanor, Yui has shown to care for her classmates, most prominently during the Forest Training Camp Arc, when she looks after Juzo Honenuki and Ibara Shiozaki after they get knocked unconscious by Mustard's poisonous gas.[1]

Although she rarely talks and has no expression, Yui isn't moody. When she's happy, she says 'Mm!' When she eats her favorite tomatoes, she says 'MM!'[2]



Size (サイズ Saizu?): Yui's Quirk grants her the ability to alter the size of nonliving objects that she has interacted with. It appears to be activated by Yui touching her fingertips together.[3]


2/6 D
3/6 C
5/6 A+
3/6 C
6/6 S
Yui's stats, according to the Ultra Analysis Book

Battles & Events

Battles & Events

Chapter Appearances

U.A. Sports Festival Arc
22. That's the Idea, Ochaco Absent
23. Roaring Sports Festival Absent
24. Mad Dash and Knockdown Absent
25. In Their Own Quirky Ways Absent
26. Chase Down the Leader Debut
27. Earth-Shatteringly Fateful Negotiations Appears
28. Strats, Strats, Strats Appears
29. Unaware Appears
30. Cavalry-Match Finale Appears
31. The Boy Born with Everything Absent
32. Smile, Prince of Nonsense Land! Absent
33. Shinso's Situation Absent
34. Victory or Defeat Absent
35. Battle On, Challengers! Absent
36. Bakugo vs. Uraraka Absent
37. Midoriya and Endeavor Absent
38. Todoroki vs. Midoriya Absent
39. Shoto Todoroki: Origin Absent
40. Emancipation Absent
41. Fight On, Ida Absent
42. Final-Match Time Absent
43. Todoroki vs. Bakugo Absent
44. Relaxing Day Off Absent
Forest Training Camp Arc
70. Wild, Wild, Pussycats Absent
71. Kota Absent
72. Day Two Absent
73. Good Evening Appears
74. Smoke Signal Appears
75. Stake Your Life, Hero! Pictured
76. My Hero Absent
77. It's Okay Absent
78. Whirling Chaos Absent
79. Drive It Home, Iron Fist!!! Absent
80. Establishing the Bakugo Bodyguard Brigade Absent
81. Roaring Upheaval Absent
82. What a Twist! Absent
83. Loss Appears
U.A. School Festival Arc
169. School Festival Absent
170. With Eri Absent
171. Gentle and La Brava Absent
172. Prepping for the School Festival Is the Funnest Part (Part 1) Absent
173. Prepping for the School Festival Is the Funnest Part (Part 2) Pictured
174. Golden Tips Imperial Absent
175. Morning, the Day Of Appears
176. Deku vs. Gentle Criminal Absent
177. At the Construction Site Absent
178. The Woman Called La Brava Absent
179. School Festival Start!! Absent
180. Unbeknownst Absent
181. For Someone Else Absent
182. Let It Flow! School Festival! Absent
183. Festival All Day Long!! Appears
Joint Training Arc
194. Cold Skies over U.A. High! Appears
195. Clash! Class A vs. Class B! Appears
196. Make It Happen, Shinso!! Absent
197. Quaotic Quirkstravaganza Absent
198. Known Where You Stand when It Counts!! Absent
199. Operation New Improv Moves! Absent
200. Clever Commander! Absent
201. Foresight Absent
202. Match 3 Absent
203. Flexible! Juzo Honenuki! Appears
204. Tuning Up Absent
205. Detour Absent
206. Match 3 Conclusion Appears
207. Early Bird! Absent
208. Match 4 Conclusion Absent
209. Match 5 Start Appears
210. The One For All Dream Appears
211. That Which Is Inherited Flashback
212. That Which Is Inherited, Part 2 Absent
213. Realm of Souls Appears
214. Our Brawl Appears
215. Final Face-Off! Midoriya vs. Shinso! Appears
216. Class A vs. Class B: Conclusion! Appears
217. The New Power and All For One Appears
Endeavor Agency Arc
241. Do That Interview! Absent
242. Have a Merry Christmas! Absent
243. Off to Endeavor's Agency! Absent
244. Recommended Reading Absent
245. Rise to Action Absent
246. Message Appears
247. Status Report! Absent
248. One Thing at a Time Absent
249. The Hellish Todoroki Family Absent
250. Ending Absent
251. Just One Week Absent
252. The Unforgiven Absent
Paranormal Liberation War Arc
253. Shirakumo Absent
254. More of a Hero than Anyone Absent
255. Hero Hopeful Absent
256. The High, Deep Blue Sky Absent
257. Pass It Forward, to Whomever Mentioned
258. Friends Absent
259. A Quiet Beginning Absent
260. Life's Work Absent
261. High-Ends Absent
262. Mirko, the No. 5 Hero Absent
263. I Wanna Be with You Guys!! Absent
264. One's Justice Absent
265. Villains and Heroes Absent
266. Happy Life Absent
267. Flames Absent
268. Scramble! Absent
269. The Three of Us Absent
270. Inheritance Absent
271. Dark Cloud Absent
272. Good Morning! Absent
273. The Thrill of Destruction Absent
274. Search Absent
275. Encounter, Part 2 Absent
276. You Cheated...! Absent
277. Who...? Absent
278. Disaster Walker Absent
279. League of Villains vs. U.A. Students Appears
280. Red Riot, Part 3 Absent
281. Plus Ultra Absent
282. Footfall of Destruction Absent
283. 75 Appears
284. Deep Blue Battle Absent
285. Katsuki Bakugo Rising Absent
286. The Ones Within Us Absent
287. Mistake Absent
288. Save Takeo!! Absent
289. Miss Candid and Miss Shut-Away Absent
290. Dabi's Dance Absent
291. Thanks For Going Strong Absent
292. Threads of Hope Absent
293. Hero-Saturated Society Absent
294. Final Performance Absent
295. Tenacious Absent
296. Hellish Hell Absent
297. Tartarus Absent
298. Sounds of Collapse Absent
299. Like Those Tragic Tales Absent
300. The Hellish Todoroki Family, Part 2 Absent
301. The Wrong Way to Put Out a Fire, Part 1 Absent
302. The Wrong Way to Put Out a Fire, Part 2 Absent
303. Top Three Absent
304. Izuku Midoriya and Toshinori Yagi Absent
305. Izuku Midoriya and Tomura Shigaraki Absent
306. The Final Act Begins Absent


Early design concepts for Yui including Ochaco and Mt. Lady.

  • Her concept is derived from Ochaco's prototype appearance and similar name and Quirk.
  • Her name contains the kanji for "small" ( ko?), "big" ( dai?) and "ordinary" ( yui?).
  • Yui's rankings on the Popularity Polls are as following:
    • Ranked 118th place in the 4th Popularity Poll.
  • The crest on the hat of Yui’s hero costume resembles Ultraseven's Eye Slugger. Ultraseven is known for changing in size, which is the same as the effect Yui's Quirk has.
    • Her hero costume's color scheme of largely red with silver streaks seems to further this connection. In addition, said costume has what appears to be a homage to the Color Timer, a special organ many Ultras have that can be found either on the sternum or on/around the sternoclavicular joint.
  • Yui was unaware that a group of boys formed a fan club for her during her middle school years, even after she graduated.[4]
  • Yui also appears to like matryoshka dolls.[5]
  • Yui's English voice actor, Madeleine Morris, also voices Komari Ikoma.


  1. My Hero Academia Anime: Episode 43.
  2. My Hero Academia: Ultra Analysis: The Official Character Guide.
  3. My Hero Academia Manga: Chapter 210.
  4. My Hero Academia Manga: Vol. 22, Omake
  5. My Hero Academia Manga: Vol. 22.

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