The mysteries don't end at Tri-Edge. Before Haseo was able to fight for himself - when he first joined the game - Ovan saved him from certain death at the hands of a Player Killer. They then became allies. While Haseo has a fiery temper, Ovan is cool and collected, and analyzes problems before acting. This is probably what led to the end of their adventures together...
After Haseo runs into Tri-Edge, he is forced to seek Ovan once again. The mysterious restraining device encasing Ovan's left arm is just one hint about what secrets he holds. He's certain to be key to the .hack//G.U. saga.