Those Who Prevent the Extermination of the World Tree

Those Who Prevent the Extermination of the World Tree (世界樹を絶やさぬ者) was a Norse Magic Cabal, one of five who united to attack Brunhild Eiktobel's cabal and were subsequently destroyed by her in revenge.

Background
Five years ago, Those Who Prevent the Extermination of the World Tree, together with the Iron Stake that Carves Knowledge, Champions from the Sea, Those who Know the Rune of the God’s Sword and the Hammer that Tempers Gold within the Earth, attacked Brunhild Eiktobel's cabal out of fear that her nature as a Saint and Valkyrie would cause pure Norse-style magic to go into decline.

After destroying Brunhild's cabal, the cabals continually pursued her. They attacked other smaller Norse cabals so they would feel threatened and not attempt to support her, and killed children with no connection to magic just for speaking to her as she lay collapsed by the roadside. They also dug up the graves she'd made for the children that were killed by their attack and fed the bodies to wolves.

The cabals eventually captured Brunhild during a period when her Valkyrie and Saint sides were equal and she was reduced to the level of a normal person. Though they loathed her, they didn't kill her as they wanted to obtain certain spells which she had gathered which ordinary people couldn't use. Instead they tortured her, not just for information but also feeling joy from it. They also had a boy, Ceillier Flatley, become Brunhild's emotional support to make the torture more effective, however as the boy became closer to her, he grew guilty and confessed his role to Brunhild. Sometime later, a cabal member came to Brunhild and grinning, informed her that Ceillier had killed himself, presenting a letter with his last apology. Enraged, Brunhild broke her restraints and escaped.

Toaru Majutsu no Index SS: Kanzaki
Those Who Prevent the Extermination of the World Tree was noted to have been active recently by the Tour Guide, around the time of the bombings carried out by the magician Leasic. It was crushed when Brunhild initiated her revenge against the five cabals.