To complete The Urge to Train side quest is extremely straightforward, though it does require some precision timing to finish it. For this quest, you need to find and defeat three Brawn Yawn while SAS Sclerokinesis is active.
Brawn Yawns can be found in the Abandoned Subway: Suoh Line 9—Inside Abandoned Line area. From where you start in the area, proceed to the opening on your right as you progress. You have to fight three Rainy Rummy's in this room before the Brain Yawn spawns further in the room.
SAS Sclerokinesis has one of the shortest active times out of all SAS abilities, so the Brain Yawn has to be almost dead before you should activate it and land the finishing blow. If you do not kill the target with SAS Sclerokinesis activated, it will not count towards the quest goal.
Once the Other is dead, teleport to a different location, not in Abandoned Subway: Suoh Line 9, then teleport back to the Inside Abandoned Line area and head to the same location. The Brain Yawn will have respawned, and you can get three kills swiftly to hand the quest.
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