Spirit Magic

"Spirit Magic is ancient, really. My great grandfather invented it. Warlocks considered it to be the purest form of magic in existence and that's why I was an abomination. I didn't play by the rules. The magic you use now, is the same magic I used and taught to the girl I loved. Didn't turn very well for me but I see modern magic is doing well, so my legacy is pretty darn good!"

- Dagrim Enkara to Timothy Gusto

Spirit Magic (気の魔法, Ki no Mahō) is an ancient Caster Magic utilized by the Warlocks that allowed them to control and manipulate the essence of spirits or borrow power from spirits themselves. The users can channel this power granted by the spirits around them to accomplish astonishing feats.

Overview
"In time, I will teach you but you must remember— the spirits are everywhere. You must feel the connection. You must connect your magic to the spirits so that they can lend you their power or let you manipulate their essence. The Earth you walk on, the water you drink, the air you breathe, all of these contains trace of spirit fragments left behind by those who died. Use it. As a Warlock, I naturally have a strong connection with the earth itself but you don't Timothy and we are going to do something about it!"

- Dagrim to Timothy.

Spirit magic revolves around channeling, summoning or using the power of spirits to achieve certain goals. While Dagrim mostly remains vague about it's usage, he did mention that spirit magic can be used to communicate with the deceased.