Arius is a boss that appears in Dante's Disc Mission 13 then appears again later in Mission 17. Lucia fights him only once in Mission 9. This boss can be random at times, but there is a specific sequence that ensures this fight goes the same way most of the time.
NG+ Note: Same strategy as New Game.
If you receive A rank on your first encounter then you got perfect Arius, otherwise you got trolled by either :
Arius No Summon Cycle
Aerial Cross Arius
This fight is unfortunately random. Because, there are additional enemies that prevents you from getting the same quick kill result as the first encounter. Consequently, you are only going to spam Stinger and hope that he doesn't do any bad patterns.
HD Collection, the fight is more consistent due to Flame Heart Glitch. If you hit Arius with Round Trip, every other enemy will get hit from the Fire element effects.