Use Tim's Hi-Combine with the guardian Raftina on Titanius in the town of Halmetz. He will almost always die instantly.

Wear him down with Magic and with Ashley's Access form. After about one to two minutes of hitting him with it, use Ashley's Dead or Alive Arm. He should die after one or two shots from it.

Make sure that you have plenty of ammunition in Ashley's guns. Use Ashley, Kanon, and Lilka. As soon as you start the battle, have Kanon use a Lucky Card on everybody. Then, have Ashley use Dead Or Alive. This will usually kill him on your first try, but if not do it again. Since you used Lucky Card, you should get a lot of experience and Gella. If this works the first time, Titanious will never have a chance to even hit you once.