"One time there was a woman so filled with jealousy that, in order to kill the person she hated, every night she would dip in the river Uji and practice a cursing ritual. She did over and over until she was able to get her revenge, but at the same time she became a full-fledged youkai. From there on, as a creature born out of jealousy, every time she was faced with a pretty woman she'd try to bring unhappiness unto her. For this reason, wedding processions would avoid the shorter path across the river and opt for the longer but safer road, to avoid angering the Bridge Princess."
Anyway, I own that book, so I could look it up. It's basically a youkai encyclopedia.
(For the record, Laevateinn doesn't belong to Loki. It's the sword wielded by the fire lord Surtr to sever the roots of the cosmic tree Yggdrasil, during the Ragnarok events. The name means "wounding wand" or "staff of destruction".)
I once saw a video detailing how the spells and danmaku patterns were designed to reflect the history of the shrine that became model for the Moriya shrine. Interesting stuff.