As he gets older, although he gains a position in the Sirius Platoon, he doesn't follow orders very well. He follows his heart instead, which constantly puts him at odds with other members, especially Bruce, and the current Captain, Schwanhelt Bulge. Due to his insubbordination, he is usually found cleaning the trains rather than being on missions.
In time, he improves and he came a great member of SDF. When Bruce died, he carried Bruce's postion when training the new recruits and he is very good at it.
Bulge state that Manabu somehow resembles his father, Yuuki Wataru even in some missions that his father perform it alone, he was impressed by Manabu's effort that that he even state him as "Like father, like son". He is most likely the stongest candidate to succed his father's seat as next Sirius Platoon Captain due to his traits.