A Gunpla Fighter who lives in Sei's neighborhood. He's constantly hatching plans to get a hold of Sei's high-powered Gunpla for his own battling use. His overbearing personality means he doesn't have many friends.
By the time of Gundam Build Fighters Try, it's mentioned that Susumu has become a famous fighter in his own right especially the quality of his YMS-15 Gyan's shield. Susumu gives a pair of said shield as gifts to both Kaoruko Sazaki and Tateo Sazaki, although it's noted that he is worried about his younger brother's future upon seeing the HG-01 Hyper Gyanko.