Lindenbaum (リンデンバウム Rindenbaumu) is Elias' magician Master, commonly referred as Lindel (リンデル Rinderu). He lives in the Land of Dragons, the last sanctuary of dragons. His title is Echoes, Song of Flowers. He was born before names, and thus his current name was given to him by Rahab.
Lindel has blonde hair which he ties in two loose strands. He wears a white hood with grey designs around the edges. Beneath that is a maroon robe. In the manga, he seems to have been able to get his hands on modern clothes, including a green hoodie.
Though Lindel is introduced as malicious he is actually a reserved individual, though playful enough to throw the occasional insult at his old apprentice, Elias.
Lindel is a magi, a being who came before man could harness the power of steam and oil. Magi were the first to see and get assistance from the fae, and can live for what seems to be millenia. They pass their knowledge which turned in to what modern society calls magic.
During his long life, Lindel grew tired of trying to find his reason for existence. He chose then to live as a nomad, carrying for caribou and growing moss while avoiding humans. During one winter, when no wolves came near his tent, Elias collapsed in front of him. After taking him to Rahab to receive advice, Lindel and Elias become friends and continued living a nomad life until an unknown time had passed and they split ways. Currently, he is the caretaker of the last dragon nest.
He has a selkie as his familiar called Merituuli (Finnish for "sea breeze").
Lindel is Elias' long term friends. They both raised caribou together up until Elias moved to Britain.
Lindel was once a student to Rahab, but while Rahab stays in touch with humans, Lindel chose to avoid humans and their conflicts. He is still able to contact her by wrapping sprigs of spruce with a red piece of yarn. She chose his name.
In a bedtime story, he tells her about Elias' past, something he avoids speaking about. While in the dragon nest, Lindel guides Chise in creating her first staff and was the elder that finished said staff, as per tradition.