Spoilers: Garena was introduced in The Trouble with Trolls.
AKA: no nicknames
Age: ~778 in year 0
Looks: Male. Usually 5'3", grey-blond hair, green eyes. Half wood nymph.
Character: Not especially socialized. ;) Truly laissez-faire attitude of non-interference.
Special skills: Strong fire healer. Weak nymph abilities include body projection, tree travel, communicates with anything, very short-range future-reading.
Family: Garena is Wolfram's secret grandfather.
Garena, Friedrich von Bielenfeld, and the famed beauty Emeraude von Bielenfeld, were treeborn triplets, offspring of the last remaining wood nymph Tariel, and Theophilus Lord Bielenfeld. Theophilus hoped to strengthen the new fire healer gift. Tariel hoped to re-establish his race. Neither got what they wanted in Garena. The triplets stayed with Tariel for a time (decades), then Theophilus took away the demonlike Friedrich and Emeraude. The more nymphlike Garena was left behind, as Tariel's companion, in the Krist Fens. The demons lost touch, though Friedrich re-established contact when they were in their 70's.
Friedrich's outrageous grandson and heir Wolfred, found that he and Aldrich both made seeds when they had sex a certain way - hardly something the youths wished to discuss with Friedrich. Wolfred consulted Tariel and Garena about it, then got sexually involved with Garena, and Manfred von Bielenfeld was the result. Wolfred took his newborn son home, and refused to explain. He married Phoebe von Bielenfeld, his grandfather Friedrich's youngest half-sister, and they claimed Manfred was their joint child. Garena and Tariel met Manfred as an adolescent, but decided to honor Wolfred's wishes and let Manfred believe Phoebe was his mother, until TwT. But if we call the seed-producer 'mother', the male-plus Wolfred was his mother, and Garena his father.
Usually sole companion to the rather depressed and dispassionate last wood nymph Tariel, bereft of the only playmates even slightly like him, Garena's socially inept. He's wandered into the demon world several times over the centuries, and had several other children with demon women. Efram's mother is descended from one of these unions. Garena gave Efram his nymph-summoning whistle.
Garena fits in nowhere, least of all with the wood nymphs after they're restored (GoT). But now he's making an effort to join society in diverse Trondheim, under Friedrich's tutelage. (Friedrich would have discouraged this in Bielenfeld.) He even has an exciting new lady-friend, 'Gwendal's dragon talker' . (GoT didn't explain, but she's Wolfred's half-sister, via his late father Wolfgang's mistress in Walde.)
Garena has the same raw fire healing gift as Friedrich, but little practice, and zero bedside manner. Tariel's body is only a physical projection of his nonphysical being, but Garena flips back and forth between nonphysical, and a physiologically authentic demon. He can communicate with any living thing (not just Mazoku). He can future-read as Tariel can, but his range is short. For instance, he can see futures that directly involve him, today or tomorrow. He can deliver treeborn babies, but can't produce seeds. Some of those strange nymph-descended gifts come of nymph genes from both parents.
There's no way to know whether Garena is mortal or immortal - he is unique. Even more so than Friedrich, he will not kill. And he'd be hard to kill, since he can go nonphysical at whim.