"Do you have any idea Ginji-san? Any idea what happened to the rest of us? Because you disappeared. And do you know what's going on in Infinite Fortress right now? And what MakubeX is about to start?" - Shu to Ginji
Shu (Shuu/Syu) was a member of VOLTS and a friend of Ginji back in times.
Shu was first seen in the I.L. arc where Akabane was supposed to kill him. Ginji stopped Akabane while Shu recognizes him.
Shu frankly told Ginji what's going on in Infinity Fortress. Later on, he was killed by Horii.
Like in the anime, it was almost the same however he was slapped by Shido. He was also killed by Horii but later on, it was revealed that he was just a Virtual Reality.
He died long time ago after Ginji left Infinity Fortress.