WARNING: The following contains spoilers for My Hero Academia Chapter 341, "The Story of How We All Became Heroes, Part Minus 1" by Kohei Horikoshi, Caleb Cook and John Hunt, available now in English from Viz Media.
As a member of the League of Villains, Spinner has faced far less action than the rest of his teammates so far in My Hero Academia. Since his Quirk was unsuited for combat or espionage, he didn't play an active role in League missions after the UA summer training camp invasion.
Spinner's inactivity allowed him to form strong bonds with all the other members, and he became the "heart" of the League garnering almost as much respect from the others as Shigaraki Tomura. In the aftermath of the war, Spinner's influence stretched past the league and in My Hero Academia Chapter 341, he has to choose how to wield his newfound power.
Born with the heteromorphic Quirk, Lizard, Spinner always felt like a societal outcast in MHA. Like many other heteromorphs, his Quirk was often viewed with disgust and fear by others with more discreet abilities. The discrimination he faced meant the opportunities available to him in society would always be limited. Spinner lived in the shadows, forever relegated to a life of petty villainy -- until he discovered Stain.
Stain's promise of complete societal reform was music to Spinner's ears. Believing the League to be affiliated with Stain, he enlisted and for the first time experienced the unconditional acceptance he'd yearned for his whole life. For a time, his entire existence was devoted to making Stain's dream a reality but the longer he journeyed with Shigaraki, the more he began to admire his leader. After a while, Spinner forwent Stain's teachings and instead threw his full weight behind Shigaraki. He took his job as the League's heart seriously and tried his best to keep the team united, even in the aftermath of the Paranormal Liberation War.
After the war, Spinner unintentionally began to attract a cult following; it turned out other heteromorphs shared the same sentiments he previously did. Stain's anti-hero message resonated strongly with them and Spinner, who proudly wore a Stain imitation costume and was a heteromorph member of the League Villains, was the perfect rallying point. It began with a few random villains copying Spinner's costume, but after the Meta-Liberation ideology was popularized during the war, quickly snowballed into a semi-organized movement that eagerly awaited Spinner's acknowledgment and leadership.
Never one to waste an opportunity in My Hero Academia, All For One instructed Spinner to take advantage of the groundswell to increase "Shigaraki's" power, and their chances of winning the upcoming war, by publicly supporting his leader. Skeptic of the Meta-Liberation Army is of the same mind -- except, he couldn't care less about Spinner or the League of Villains. He just sees them as a tool to rekindle the flames of Meta-Liberation. Their support for Spinner isn't based on actual belief in his competence but to further their own goals. Incidentally, this may come back to bite them in the near future.
In the end, the one with the actual social capital among the heteromorphs is still Spinner. His alliance with All For One hinges on the lie that Shigaraki is still whole and completely himself. Spinner already has his misgivings about his leader's current state, but finding out that All For One is steadily eroding Shigaraki's consciousness will completely destroy any alliance they might have.
Spinner might even end up co-opting the Meta-Liberation idea to make positive change in the future for other heteromorphs without all the societal upheaval Skeptic is looking forward to. Whatever he decides to use his influence for, Spinner's decisions moving forward are sure to influence My Hero Academia greatly.
