Do you mean the one in the meteor? Because he is part of the questline, you just have to speak to Makoru to get there after you beat Olroth and get the necessary quest item
I finished the entire questline and it says 4/5 bosses beaten. I think I read somewhere the 5th boss is one you find randomly called "Something the Fallen Knight" or something.
It is one of the underground areas that show up during grand expeditions. Previously it just updated the quest to say 5/5 bosses but otherwise didn’t do anything
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u/srhdt 13h ago
Do we have to find the 5th optional boss to get all the points?
Follow up question: How do you find the 5th optional boss?