Win qualis = ch6 budokai map -> go to west ( budokai gambler ) and there is NPC which teleport you to korin city -> use it so you are in korin ch6, same as your friends -> do HTB bug with pet call -> now you are immortal on ch6 ^^
It working till someone HTB u in fight.

Now i can tell it coz bug gone :)

Yes, but every time you enter a round in budokai your buffs, lp and ep reset, so I doubt that would have even worked.