Squad Mike (ミケ分隊 Mike-buntai?) was a major division of the Survey Corps led by Squad Leader Mike Zacharias. They were placed in charge of the suspected Survey Corps recruits at the time of the Wall Rose invasion.
As veteran members of the Survey Corps from before the Fall of Wall Maria, Squad Leader Mike Zacharias and his subordinate Nanaba are made aware of Commander Erwin Smith's plan to capture a Titan spy during the 57th Expedition Outside the Walls. While Nanaba supervises the Survey Corps recruits at the edge of the Titan Forest, Mike joins the capture team further within. When the Female Titan is captured with the Corps' special target restraining weapon, Mike and Captain Levi attempt to dismember the hands guarding the Female Titan's nape, only to find their ultrahard steel blades are ineffective against the Female's hardened crystalline skin. Before explosives can be brought out to remove the hands, the Female Titan screams. Soon afterward, Mike smells incoming Titans from all directions, and the Survey Corps soldiers are forced to eliminate the Titans devouring the Female Titan. Despite their efforts, the Female Titan's pilot escapes and Commander Erwin orders for a retreat to Karanes District.
Shortly after the failed expedition, Commander Erwin entrusts Mike and his squad with watching the new recruits in the Survey Corps in Wall Rose, excluding some trusted recruits who would partake in an attempt to capture Annie Leonhart, suspected of being the Female Titan, in Stohess District. Two days later, on the day of the Stohess District operation, Mike's squad sights incoming Titans inexplicably within Wall Rose. Mike immediately sends his subordinate Thomas to warn their comrades in Stohess District of the sudden Wall Rose invasion.
Admitting that there are likely no Titans among the 104th Survey Corps, Mike observes the incoming Titans while Nanaba warns the recruits of the invasion. She tells the cadets to prepare to depart immediately, before returning to Mike. They regret putting the 104th into the dangerous situation unprepared, and discuss the breach of the Wall. When Nanaba laments the hopelessness of the situation, Mike reassures her that humanity will not lose if they continue fighting.
Once the 104th finish preparing, the group rides out, with Mike coordinating a plan to split into four teams and spread the word throughout the Walls. Once a group of nine invading Titans reach the nearby woods, the four teams scatter in different directions. When the Titans accelerate, Mike splits off from the southern team to single-handedly engage the group, and leaves Gelgar in charge of the team.
Mike kills 5 of the 9 Titans before deciding to depart. However, as his horse rides back to him, a Beast-like Titan picks it up and throws it at him, knocking him from the roof into a nearby Titan's mouth. After questioning Mike, the Bestial Titan takes his maneuvering gear and goes to leave. Remembering his reassuring words to Nanaba, Mike steels himself, but is killed helplessly when the Beast Titan sets the other Titans on him.
Squad Mike continues to spread the word throughout the Walls, with Tomas getting word to Commander Erwin in Stohess. Seven hours after the Titans were spotted, the western team led by Nanaba and Henning head towards the Wall to determine the location of the breach. Two hours later, the southern team reaches Ragako, where they find the village empty, yet destroyed by the Titans. Lynne theorizes that the villagers had escaped, though Gelgar silently disagrees. Trying to get Connie Springer away from the Titan atop his house, the team swiftly departs to search the Walls.
After the sunset, the two teams separately navigate in the dark by torchlight. Terrified of the hidden threat, the two teams come across one another, with neither team having found the breaches location. Both teams agree to rest at the ruins of Utgard Castle nearby, and to continue the search the next day. The four present members of Squad Mike agree to keep watch from atop the tower, and prepare for a long night.
In the middle of nightfall, Lynne announces that Titans are moving outside the castle. After spotting the Beast Titan moving towards the Wall, the senior soldiers leap into battle, and maneuver around the tower to combat the wave of Titans. After seeing Titans had made it inside, Lynne has the cadets immobilize the Titans within the tower.
Lynne, Henning and the horses are all killed when the Beast Titan hurls several chunks of the Wall at the castle. It then summons a second, larger wave of Titans to continue the attack. Nanaba and Gelgar continue fighting the Titans, with a shortage of gas and blades. However, Gelgar hits his head at some stage. He praises themselves on doing a good job, and falls down towards the Titans. Nanaba manages to temporarily save him, but her gas runs out and she is left stranded. With this, both veterans are devoured by the Titan horde.
In the Battle of Shiganshina District, Erwin Smith contemplates his actions as Commander, and considered the ways he had fooled his comrades. He begins to envisage himself atop a mountain of corpses, representing the soldiers he had sent to their deaths. At the top of the mountain is Mike, alongside Nanaba and Gelgar, who stare back at Erwin. Later in the battle, Erwin laments the dwindling hope of his dream, but thinks back to Squad Mike and the other fallen soldiers, who wonder if their deaths had meaning.