Rui had no intention of making an appearance in the battle. That was highly unwise on his part. His intentions were to make a highly injured appearance at the Deacon Industries main branch after the other three survivors returned alive, giving off the impression he just barely managed to escape a bloody battle with his life intact.
The only reason he was still waiting around and watching was to jump in and save Kane if anything happened even by mistake. Even though Kane was pretty much impossible to sense in the Shionel Dungeon, that did not make him invulnerable. Kane was so weak that even a single attack from any of these high-grade Martial Squires could kill him. If a single attack from these A-rank Martial Squires fighting all out hit a vital area, the sheer damage might instantly kill him.
