WARNING: The following contains spoilers for Season 4, Episode 7 of Attack on Titan, "Assault," now streaming on Crunchyroll, Funimation, Amazon Prime and Hulu.
Episode 7 of Attack on Titan Season 4 is the largest Titan brawl in the anime's history, with almost every one of the Nine Shifters going head-to-head in the Marleyan Internment Zone. While the Attack, Beast, War Hammer, Jaw and Cart Titans duke it out in Liberio, away from the action, but still completely unmissable, is the Colossal Titan. More specifically: Armin Alert's Colossal Titan, marking the Titan's reintroduction to the series for the first time.
One of the biggest upsets at the end of the Attack on Titan anime's third season was the Colossal Titan changing hands. Previously held by Bertolt Hoover, a Marleyan Warrior, Armin was revived from the brink of death with a vial of Titan spinal fluid after suffering severe burns from the Colossal Titan's defensive steam. Consuming a defeated Bertolt to spare himself becoming a Pure Titan, Armin inherited the very power that kicked a hole through Paradis Island's wall years before, changing his life forever.
In "Assault," Armin turns this power back on the people who sent Bertolt to his home in the first place, playing an extremely important role during the invasion of Marley -- in more ways than you might realize.
In Episode 5, Armin appeared to be the one -- hidden by a cloak -- to lead Pieck Finger (the Cart Titan) and Porco Galliard (the Jaw Titan) into a trap. In Episode 7, he's revealed to have headed to Marley's docks afterward, rather than join Eren and the rest of the Scouts in battle. There, he rows himself right into the middle of the military's boats and unleashes his Titan form for the first time (that we've seen). As the Colossal Titan is one of the lesser-used Shifters, due to its size, it's easy to forget how devastating simply manifesting the form is. Armin more than reminds us of that here. The resulting force not only obliterates most of Marley's naval fleet and surrounding barracks but also sends gusts of hot wind through the nation's nearby streets for miles around. When the Colossal Titan shows up, everyone knows about it.
The strategy behind this is two-fold. Firstly, with most of the nation's armed forces gathered at the docks to invade Paradis Island, Armin just set them back by months, maybe even years. In the present, it also buys Eren and the others extra time to make their airborne getaway while their enemy scrambles to regroup. But you only have to listen to Peick and Porco's bitter exchange of words to understand the psychological impact this reveal has, too, as it's confirmed that the Colossal Titan has indeed fallen into the other side's hands.
There's little reason to doubt that while Eren planned this entire attack to steal more Shifter powers from Marley, he also wants to flex on an enemy that has been torturing his people for decades. Leading Reiner Braun (the Armored Titan), for instance, into a basement was another trap, but his monologue beforehand? Eren wants Marley to know that revenge is a dish best served when you least expect it. The presence of the Colossal Titan under Eldian control is both a demonstration of might and a chilling warning to those who oppose Eren.
Armin himself, however, is as introspective as ever even with his new incredible power. Emerging from the Colossal Titan, he sullenly observes the wanton destruction and loss of human life using the form has caused -- much like we saw Bertolt himself do in Episode 4's flashback. This grim-faced view of what the Corps is doing in Marley is something also reflected in Mikasa and Jean, reinforcing the idea that there's a clear divide between Eren and his comrades. Perhaps it's fitting that a Titan as ruinous as the Colossal Titan tends to be held by thinkers rather than doers, as choosing to use it requires a level-head. The true tragedy might be what wielding such a godly force of nature might do to Armin, the gentlest of the Scouts.