Warning! Spoilers for My Hero Academia Vigilantes Chapter 103 ahead!
The My Hero Academia spinoff manga, My Hero Academia Vigilantes, has offered a view into a very different part of that series' universe, and one of the most exciting aspects has been a chance to see All Might in his glory days. While All Might has been used sparingly in the manga so far, it seems that the situation has finally become dire enough that it's time to call in the man himself in chapter 103.
In what seems likely to be the manga's final arc, Koichi has been facing off against the mysterious being known as Number Six, who seems to have been an experimental Nomu gone awry. Number Six has become extremely possessive of Koichi's fellow vigilante Pop Step, whom he briefly brainwashed into becoming a villain, which ultimately landed her in the hospital. Now Number Six is at the hospital to finish her off, and runs into a police force led by All Might's friend on the force, Detective Tsukauchi. They manage to get handcuffs on him, but Number Six has become so divorced from his human origins that he's able turn himself to ooze and escape his bonds. As Koichi arrives on the scene following an impressive jump across town, Tsukauchi is willing to overlook his vigilante activities in order to give him a message: Call All Might.
All Might last had a major appearance during the Tokyo Sky Egg arc, more than fifty chapters ago, where he arrived just in time to prevent a building from collapsing with thousands of people trapped inside, including Tsukauchi's sister. Koichi and American hero Captain Celebrity still did most of the work during that ordeal, but All Might's timely arrival was critical to saving lives. It was also revealed, at that time, that All Might was already suffering from the injuries he's seen with in the first chapters of My Hero Academia, although no one but Tsukauchi knew about it. While All Might had previously told Tsukauchi not to hesitate to call him, the detective had declined the offer, since he feared their connection might become public and would result in attempts on his life. The Sky Egg incident has so far been the only time Tsukauchi went back on this, so the situation at the hospital must be pretty serious in his opinion.
While Koichi takes off to deliver the message, it's not clear whether or not he actually manages to do it, as he's last seen at the end of the chapter returning to face off with Number Six. It's possible Koichi fired off a projectile, made a phone call, or did something else that would get All Might's attention before turning around. And after all, Koichi ultimately headed to the hospital to protect Pop Step, and he isn't about to leave her now. At least one pro hero, Midnight, is already present at the hospital, but she and All Might don't appear to know each other yet.
Should All Might arrive, it's also likely that it won't be until after Koichi has had his chance to face off with Number Six, as this is a fight that's been a long time coming. Still, while All Might could be seen as a Deus Ex Machina, it would be fitting for Koichi to fight at his side in the end, as he has looked up to All Might throughout My Hero Academia Vigilantes. Fans can only hope that they'll get to see the musclebound hero in action one last time, even if it's technically a prequel.