Also known as: possibly Houjou Ujihide (北条氏秀), Houjou Saburou (北条三郎), Saburou Kagetora (三郎景虎)
Historically: Uesugi Kagetora was the seventh son (sixth to survive to adulthood) of Houjou Ujiyasu, younger brother of Houjou Ujimasa, Houjou Ujiteru, Houjou Ujikuni, Houjou Ujinori, Houjou Ujitada, and older brother of Houjou Ujimitsu. His mother was the sister-in-law of Tooyama Yasumitsu, a vassal of the Houjou Clan (other sources say Zuikeiin, Ujiyasu's principle wife). It's likely that he and Houjou Ujihide were two different people and that Ujihide was the son of Houjou Tsunashige and living in Edo while Saburou was living in Echigo, so most historians refer to him as Houjou Saburou when describing his early life.
As a child, he was sent into the priesthood at Souun Temple in Hakone, then sent as hostage to Takeda Shingen of the Takeda Clan in the three-way alliance between Houjou, Takeda, and Imagawa formed in 1554 (though this last point is now in dispute, as it is told only in the Records of Ancient Battles of the Eight Kanto Provinces and recorded in none of the Takeda Clan records.)
He was adopted by his uncle Houjou Genan in 1569 and married Genan's daughter.
When the Houjou and Uesugi clans formed an alliance in 1569, Saburou was sent to Uesugi Kenshin in an exchange of hostages with Kakizaki Haruie. (At first, the hostage was set to be Houjou Ujimasa's third son Kunimasumaru, but Ujimasa could not bring himself to send off his son, who was then still a baby.) Saburou was sent to the Uesugi clan in early 1570. Kenshin, who never married, developed a liking for the handsome and intelligent Saburou. He married his niece Seienin, the daughter of Nagao Masakage and older sister of Nagao Akikage (Uesugi Kagekatsu) to Saburou, gave him the name Kagetora (a name that had once belonged to Kenshin himself), and adopted him into the Uesugi Clan.
When Kenshin died suddenly in 1578 without naming an heir, Kagetora and Kagekatsu, similarly adopted by Kenshin, fought for succession to the position of clan head (the Otate no Ran). Though Kagetora held the early advantage with the backing of Uesugi vassals such as Uesugi Kagenobu, Honjou Hidetsuna, Kitajou Takahiro, and the Houjou Clan, the tide of the battle turned with Takeda Katsuyori's betrayal to Kagekatsu's side.
When the Otate fell in 1579, Kagetora attempted to escape to Odawara Castle, but was betrayed at Samegao Castle by Horie Munechika and committed suicide. His wife committed suicide along with him (though there are also accounts that she remained behind at the Otate and committed suicide there when her brother Kagekatsu refused Kagetora's surrender.) His oldest son Doumanmaru died at the hands of Kagekatsu's troops along with Uesugi Norimasa, and the rest of his children were believed to have died along with their parents.
In Mirage of Blaze: He was born to Houjou Ujiyasu and Zuikeiin as their eighth (seventh to survive to adulthood) and youngest son. After his death in the Otate no Ran, he was charged by Uesugi Kenshin to become kanshousha in order to ensure that the peace of Japan is not disrupted by the onshou as the leader of the Yasha-shuu and the commander of the Meikai Uesugi Army.