Shinan Esashi is the name I have given to the long haired boy with extending fingures that we saw in chapter 1 (episode 1 and 2 of the anime) and who shows up in Izuku and Bakugo's flashbacks. This guy was one of Bakugo's followers who helped beat up Izuku when they were kids.
Althogh this character technically does exist in the manga and anime he was never given a name or developed. Everything you read below about Shinan Esashi is my own invention.
History[]
Growing up Esashi admired Bakugo's strength, intelligence. and determination the same way that Izuku did but unlike Izuku never tried to stop Bakugo from hurting anybody and instead would always join in. Shinan Esashi didn't believe he could ever stand at the top or be on the same level as Bakugo, but that didn't matter because he still saw himself as superior to Izuku and took comfort in believing that Izuku would always be beneath him. This ironically encouraged a sense of complacency in Esashi that would come back to bite him later. Shina Esashi thought it was funny that a quirkless loser like Izuku thought he stood a chance at becoming a hero. As far as Shinan was concerned, torturing Izuku was an entertaining but ultimately pointless diversion. Shinan would sometimes question why Bakugo even bothered.
After the attack by the Sludge Villain, Shina Esashi felt embarassed that he had been unable to protect either himself or Bakugo and that Izuku had shown more courage than he did. Instead of this making Shinan admire Izuku however it just made him envy and resent Izuku.
While Izuku was doing his training regime with All Might. Shinan Esashi was doing a training regime of his own trying to develop his quirk and learn the best way to use it in combat. After middle school when Izuku took the entrance exam to UA, Shinan Esashi applied for Shiketsu High School and took their test but Shinan failed on both the practical and written. He failed the practical because he didn't save somebody whow as right in front of him.
Unlike Izuku. Shinan Esashi's desire to become a hero was more of a daydream than an ambition, so at the time his failure to get into Shiketsu wasn't that big of a deal. Later on however after the USJ incident when Class 1-A was in the news, Shinan saw that Izuku Midoriya had successfully gotten into UA and that was what made his own failure to get into Shiketsu so insulting.
Later on during the UA Sports Festival his jealoisy of Izuku was compounded when he watched the UA Sports festival and saw Izuku make it almost to the end.
Triggerhappy Arc[]
When Izuku Midoriya and Shinan Esashi run into each other again both of them have changed significantly and both of them have become a lot stronger. Shinan Esashi has developed a crude and agressive persona obviously trying to imitate Bakugo and has become the leader of a group of delinquints called Triggerhappy (トリガーハッピー) because they use the quirk enhancing drug known as Trigger. Unlike Bakugo who is genuinely prideful and violent, Shinan Eashi is hiding his insecurities behind bombast and his fear behind agression. The more laid back condescending attitude he exhibited during Junior High resurfaces though whenever he is feeling genuinely confident.
Quirk and abilities[]
Extended Finger (延長指, enchō yubi): allows Shinan to elongate, manipulate, and retract his fingers. Shinan can control size and direction of his fingers at will. Shinan can use his fingers to attack at a distance or help him maneuver. Shinan can use his fingers to wrap around his opponents to grab them or immobolize them. They are strong enough that they can pierce materials like rock and concerete and being hit by one is like being hit by a bullet. They are also strong enough to support his own weight, allowing him to travel through the air by swinging around on them similar to how Hanto uses Tape. Shinan can also use his fingers to attack or maneuver similar to how Moonfish does with his teeth.