This Keisuke is post-Lockdown, and a canonmate of
demoncompkid.
While Michi, Atsuro, Kaido, Mari, and Naoya were climbing the tower in Roppongi and fighting the last Bels, the angels, and Babel, Keisuke took Midori and Yuzu with him to try to find a place to hide. Along the way, they encountered panicked demon tamers (that they stopped) and malicious demons (which they also tried to stop).
The group survived, and reunited with the main group after Michi had announced his title and fallen asleep. Atsuro asked Keisuke to stay with them, but Keisuke refused. He still couldn't bring himself to fight against God, despite what he had seen. Atsuro then asked if he could contact Keisuke to keep him informed, and Keisuke responded with "you can, but he can't." He being Michi, in this case.
After that, Keisuke left, taking Midori with him. Yuzu traveled between the two groups, keeping both of them informed. When she told him what had happened to Naoya, Keisuke considered going to visit Michi - but decided against it. They'd just end up arguing.