I found this in a fantasy manga. I separated them by text bubbles.
既に手段が目的化して久しい
お互い魔力供給をしたいが為に
毎日真面目にクエストに勤しむ
そんな毎日を送っている
It's the first line I'm confused with here. Is he saying "the purpose for this changed a long time ago?"
If so, how does that connect to the next lines? Are those the original "purpose" he was talking about?
Is he saying he needs to supply magical power to do quests?
「～～て久しい」 means "It has been long since..." "It's been quite a while since..."
「手段が目的化して久しい」 means "It's been quite a while since our method turned into our purpose" (≂ 手段が目的に変わってから長い時間が経っている）
And the 手段, 目的 refer to 魔力供給. Initially 魔力供給 was their method to accomplish their original purpose (unmentioned here), but it turned into their purpose at some point in time (while they were doing quests, or fighting?)
So they say お互い魔力供給をしたいが為に毎日真面目にクエストに勤しむ, "Just for the purpose of supplying/filling up/replenishing our magical power (rather than to accomplish our initial purpose), every day we devote ourselves to our quests."
