Pu (ぷう, Pū), or Pusuke (ぷう助, Pūsuke), known as Puu in the English anime, is Yusuke's spirit beast.
Pu is a small, beady-eyed, bird-like creature with an all blue body, whitish-blue belly, a yellow beak and feet, tiny "arms" and a small patch of black hair on his head which mimics Yusuke's hairstyle. His ears are big and floppy, but long enough to be used to fly. After Yusuke's revival, Pu evolves into his "adult" appearance, transforming into a gigantic swan/phoenix-like bird with a long neck, large wingspan, elongated ears, a long horse-like black mane and large tail-feathers. In this form, Pu becomes large enough to be ridden by at least four people.
Pu, being a spirit beast, mimics the personality of its master. However, in contrast to Yusuke's slacker badboy attitude, Pu is actually very sweet. This is due to the fact that he's a reflection of Yusuke's true self deep in heart. He helps Yusuke get through his spirit orb training, as well as leads Keiko to find Yusuke should he ever be in trouble. Pu also represents Yusuke's inner purity and innocence.
Spirit Detective Saga
Yusuke received his egg early and was told by Koenma that a spirit beast would feed off its owner's energy and take its form based on the nature of the energy. In other words, if Yusuke is good, the creature inside it would reflect Yusuke. If Yusuke is evil, the negative energy would turn the creature inside the egg evil. And when it would hatch, the beast would eat Yusuke, leaving nothing, not even a spirit. Yusuke sacrifices his egg to save Keiko during an incident at Yusuke's apartment.
Dark Tournament Saga
Koenma revealed the egg wasn't destroyed. The egg did eventually hatch though, and proved to be good. Although he hated Pu first, Yusuke grew to love the little beast after he worked so hard to get Yusuke a drink of water when he was undergoing Genkai's spirit wave orb test. Yusuke normally leaves the task of watching Pu to Genkai or Keiko, who both enjoy the job. Pu was shown protecting Botan, Keiko, and Yukina from Younger Toguro's corrosive demon energy by creating a powerful shield made up of Spiritual energy.
Chapter Black Saga and Three Kings Saga
While fighting Shinobu Sensui, Yusuke's ancestor, Raizen, took over his body. His demon genes awakened, Pu evolved into a more realistic-bird with wings and grew powerful enough to withstand the attacks of the Spirit Defense Force, each member ranging from Mid A class to Upper A class while protecting Yusuke, Strongly implying that Pu reached Upper A class since he is Yusuke's Spiritual Beast. Pu is Yusuke's ride to the Demon World for the final confrontation against Sensui. His appearance didn't change, though, even when Yusuke overcame Raizen's control. Genkai took him back to live with her, where he stays in her back yard. Strangely enough, Pu takes the form of Yusuke's spirit energy, a phoenix, as seen in the final round of the Dark Tournament.
Pu in his small form appears in a cameo during the Three Kings Saga in the battle between Yusuke and Yomi.
Near the conclusion of the manga, Genkai possesses Pu as she did during Yusuke's fight with Toguro after her death. She gives words of confidence to Yusuke, who attempts to disarm a weapon capable of destroying the Earth which has been set in place by a cult who has taken Spirit World's residents hostage. Genkai then tells Yusuke to press which button he feels like, hoping the one he presses will disarm the weapon.
- Connection to Yusuke: As Yusuke's spirit beast, Pu is connected to him in mind, body and even soul. Thus he feels whatever Yusuke feels, both physically and emotionally. If and when Yusuke dies so will Pu. Due to their connection, Pu is also always able to sense Yusuke's presence, even when miles away, Pu is always able to find Yusuke no matter where he is.
- Barrier: Pu is able to create a protective barrier.
- Immense Durability: When Yusuke was in the middle of reviving from Sensui's attack in the cave, Pu shielded Yusuke with his body, and without a barrier, from an onslaught from six of the nine members of the Sprit World Special Defense Force, which is powerful enough to defeat any A Class Demon. Also, rather than fly to Yusuke via the passageways to the under ground cave where Yusuke was located, he simply smashed through the several feet of rock (he flew through the recently carved hole in the ground) to reach his partner.
- In Episode 41 of Hunter x Hunter (2011), Neon Nostrade is shown carrying a keychain figurine of Pu.
- There are similarities between Pu and Yun from Toriko, in which case the latter can be based or inspired by Pu.
- Pu being reborn as a phoenix (itself a symbol of rebirth) and Yusuke's Reiki taking the form of a phoenix both foreshadow Yusuke's awakening as a demonkin.