WARNING: The following contains spoilers for Season 5, Episode 20 of My Hero Academia, "My Villain Academia," now streaming on Funimation, Crunchyroll and Hulu.
An earlier episode of My Hero Academia depicted a reborn Tomura Shigaraki wreaking havoc on a nearby city, but he didn't reach that level of strength overnight. He had to earn it, and Season 5, Episode 20 makes it clear Shigaraki must undergo the trial of his life to earn new power from Dr. Garaki. But he faces significant obstacles to do so.
Shigaraki has an uneasy relationship with the Meta Liberation Army's leaders, and while he fights the colossal Gigantomachia, he realizes the League of Villains may soon fight a two-front war. So Shigaraki devises a resourceful counterattack involving Gigantomachia and his massive brute strength.
All For One entrusted Shigaraki with Gigantomachia and Dr. Garaki, but like MHA protagonist Izuku Midoriya, Shigaraki cannot accept all this power without proving his worthiness first. Dr. Garaki challenges him and his allies to face the titanic Gigantomachia and subdue him in combat, but even after weeks of fighting, they haven't yet completed this task. Gigantomachia is slow but incredibly durable and persistent, and fighting him eats up all of Shigaraki's free time. Aside from the fierce Dabi, the entire League of Villains finds itself dedicated to the Gigantomachia battle, allowing the Pro Heroes to pull ahead in the war against villainy.
Twice receives a phone call from Giran's phone, but to his shock, it's actually Re-Destro of the Meta Liberation Army on the line. He explains he's been tracking the League's movements and declares his intention to crush the League to mark the start of the Army's revolution. Shigaraki, being his stubborn and defiant self, accepts the challenge and makes a plan to destroy Re-Destro, probably as punishment for defying the League. He can be aggressive and childish at times, but he has also recently acquired leadership skills and cunning to make him a true villain kingpin in My Hero Academia. This is not the same Tomura Shigaraki who raided the USJ complex.
Re-Destro specifies Deika City as the venue for the confrontation, and with over 110,000 Army members across Japan to back him up, he's confident he can wipe out the numerically inferior League of Villains -- especially with the captured Giran as bait. But Shigaraki has a surprise in store: he's since realized that Gigantomachia can sense and track him anywhere, so he will proceed to Deika City to confront the Meta Liberation Army's members. Gigantomachia will follow him there, then take on the entire Army by himself.
Shigaraki cannot defeat the Liberation Army alone and isn't vain enough to try. Instead, he shows the resourcefulness of an underdog protagonist by throwing his enemies against one another in his mind, confident that Gigantomachia will slaughter every last Army member. Any survivors should be easy to mop up while the wounded and exhausted Gigantomachia will be easy to finish off too. If this strategy goes as planned, Tomura Shigaraki can ensure the League's dominance in the criminal underworld, finally completing Dr. Garaki's challenge as My Hero Academia Season 5 continues.