Shigaraki’s Transformation and the Role of All For One

Shigaraki has been observed to undergo significant changes, becoming a formidable force in the world of Boku no Hero Academia. All For One, the mastermind behind many events, has acknowledged that Shigaraki has not yet made the right choices since this transformation began. All For One further emphasizes that he is the one who has influenced Shigaraki into believing that he has chosen his own path, while in reality, All For One has been manipulating his life from the very beginning.
All For One has also revealed that the only missing element in Kosei’s plan is the “iron will.” Ultimately, Shigaraki encountered Tomura’s father, leading to a unique opportunity to shape his son’s future, especially since Tomura’s daughter, Hana, had grown too old for All For One to handle as he wished.
All For One’s Manipulation of Tomura
The next phase involves All For One bringing Tomura back home, giving him the initial Kosei and presenting him with a new version of Kosei. This new Kosei is dubbed Phân rã (Dismantlement), and it serves to test the reconstruction abilities of Kosei. Once Phân rã is handed over to Tenko Shimura/Tomura Shigaraki, All For One effectively takes control of that character’s life from the start.

Current Events in the Series
Returning to the present, Tomura Shigaraki appears as merely a shell of himself, as his mental state suggests he is still under All For One’s influence. It has been declared that Tomura has died, yet this chapter serves as a reminder that All For One will continue his plan to dominate the world, despite Deku’s determination to prevent any further destruction.
Deku finds himself in a state of despair and pain. The aftermath of Shigaraki’s mental turmoil has notably affected Deku’s right arm, resulting in significant injury and preventing him from continuing the fight. The situation has become critical, but soon after, Deku’s allies arrive to confront All For One, concluding this chapter.

Source: Reddit