Bokusenō

was a wise tree yōkai and ally of the Inu no Taishō who would use the wood from Bokusenō's own boughs to craft the scabbards for two powerful swords, the Tessaiga and the Tenseiga. Bokusenō was familiar with the Inu no Taishō's designs and was the only one of his allies or vassals who got along with the Inu no Taishō's eldest son, Sesshōmaru. As such, Bokusenō is instrumental in developing Sesshōmaru's understanding of Inuyasha's hanyō nature and the connection between Inuyasha and the Tessaiga. Bokusenō was also the means by which the Tenseiga was delivered to Sesshōmaru, since the Inu no Taishō's vassals were too afraid of Sesshōmaru to deliver it themselves. Because of the information Bokusenō gives Sesshōmaru on Inuyasha's demon blood, Sesshōmaru ultimately gives up on his quest to claim the Tessaiga and allows his younger half-brother to maintain possession of the sword.

History
Bokusenō was originally a simple, but as he grew older he eventually gained additional powers and transformed into a yōkai, similar to how kitsune and bakeneko start out as ordinary foxes and cats, respectively. Because of his great powers and wisdom that had accumulated throughout his 2,000 years of life, Bokusenō became an important ally for the Inu no Taishō, a powerful dog daiyōkai who had two swords of great power crafted from his own fangs, the Tessaiga and the Tenseiga. In order to contain their extraordinary powers, the Inu no Taishō sought out Bokusenō to beseech him for the use of the wood from his very own boughs to use as sheathes. Since the two swords possessed such awesome powers, no ordinary would could suffice. Bokusenō consented, and the craftsman Tōtōsai created two sword sheathes for the Dog General's swords. These sheathes had strange powers of their own, as would anything crafted from the wood of such a powerful tree, and would prove invaluable to their users over the years. It is unclear what relationship Bokusenō had with the Inu no Taishō beyond the provision of his wood for the sword sheathes, but as Bokusenō would later reveal, he had intimate knowledge of demon lore and of the Inu no Taishō's sons in particular, despite his sedentary nature. Whether this was because he was close in the Dog General's counsels or was simply capable of discerning such things through his own wisdom is unclear.

Later, after the Inu no Taishō died in battle, Tōtōsai bequeathed the Tenseiga, the Sword of Healing, to the Inu no Taishō's eldest son, Sesshōmaru, as was the Dog General's dying wish. However, because Tōtōsai had a great fear of Sesshōmaru, he gave the sword to him indirectly by hanging it along with a posted note on Bokusenō's trunk, much to the magnolia tree's frustration, implying that it was done without his consent.

Some 200 years later, Sesshōmaru sought out Bokusenō to inquire about the connection between his younger half-brother, Inuyasha and the sword Tessaiga, which had been given to Inuyasha as the Tenseiga had been left to Sesshōmaru. Bokusenō was surprised that Sesshōmaru would request information about his younger brother, whom Sesshōmaru despised and never talked about. But Sesshōmaru explained that twice he had witnessed a transformation in Inuyasha's scent, from that of a hanyō to that of a full-fledged yōkai, specifying that Inuyasha's blood had the same scent as both Sesshōmaru himself and his father. Bokusenō, however, was incredulous, explaining to Sesshōmaru that, as an individual born from a human and a demon, Inuyasha could never become a full-fledged demon. He continued to tell him that there was something that he, Sesshōmaru, as a pure-blooded demon, could do that Inuyasha, as a half-demon, could not. If Sesshōmaru ever found himself in a desperate situation, he could maintain his composure and remain in control of himself, but Inuyasha, as a half-demon, would be overcome by his own demon instincts as a sort of last-ditch defense-mechanism if backed into a corner. Elaborating further, Bokusenō revealed to Sesshōmaru that the blood of his and his brother's father was too powerful for a mere half-demon to control and when asked by Sesshōmaru what the outcome would be, Bokusenō told him that with repeated transformations, Inuyasha's soul would ultimately be consumed by his demon blood, causing him to degenerate into a mindless killing machine, unable to distinguish friend from foe, who would continue to kill indiscriminately until he himself was destroyed. This is why, Bokusenō concluded, Sesshōmaru's father had left the Tessaiga to Inuyasha, to ensure his youngest son's survival and prevent Inuyasha's human soul from being consumed by his demon blood.

Sesshōmaru immediately left to confirm Bokusenō's words and test Inuyasha's power while transformed. After doing so, in an apparent act of mercy and pity, Sesshōmaru spared Inuyasha's life and allowed him to retain possession of the Tessaiga, and would only challenge his ownership of the sword once more, much later, in order to confirm that he was worthy enough to wield it.

Physical description
His face emerges from the surface of his trunk and he can grow arms from his trunk at will.

Manga vs. Anime

 * In the manga, Bokusenō grows an arm so that he can rub his chin thoughtfully, while in the anime this is not shown. It is possible that this ability was shown in the manga in order to convey Bokusenō's pensiveness while mulling over a question of Sesshōmaru's, while in the anime this could be conveyed through the voice actor's tone of voice alone, and therefore was not necessary in the anime. Combined with the fact that Bokusenō only uses his arm once and then it disappears immediately afterwards, it might have made animating the scene awkward and confused viewers had it been retained.

Trivia

 * While in the English dub, Bokusenō is referred to generally as a "," he is more specifically a member of the  species of the magnolia genus. This is indicated by Sesshōmaru referring to him in the original Japanese version of the anime and manga as a hōnoki (ホオノキ, 朴の木) which is the name for a specific species of magnolia tree indigenous to Japan, known colloquially as the Japanese bigleaf magnolia, or, alternatively, the Japanese whitebark magnolia. A generic magnolia tree would have simply been referred to as mokuren (モクレン) or magunoria (マグノリア). Coincidentally, the wood from a Japanese bigleaf magnolia is strong and light and therefore popular with craftsmen in Japan, making Bokusenō's contribution of his own wood for the sheathes of the Tessaiga and Tenseiga a logical choice.