His owner was Sadayasu of the Adachi Clan during the Kamakura period, who was drawn into the political rivalry between his clan of samurai and the regent of Shogunate, Hojo Sadatoki (which resulted in the Shimotsuki Incident). Because of the Shimotsuki Incident his owner was killed by Hojo Sadatoki, who was 14. Tsurumaru was supposed to sleep in his owner's grave but Hojo Sadatoki desired this beautiful sword and he dug him out of Sadayasu's grave to take him.
Tsurumaru stayed on in the Hojo family, but the Kamakura Shogunate reached its downfall during the reign of Sadatoki's son, Takatoki. Sadatoki's grandson Tokiyuki, the last in line of the Hojo Clan, was killed by Ashikaga Takauji, who formed the new Muromachi Ashikaga Shogunate.
Tsurumaru went into unknown hands after the extermination of the Hojo Clan until he was presented to Oda Nobunaga, who then passed Tsurumaru to one of his most-valued retainers: Mori Yoshinari.
As time went by, Tsurumaru was passed around by owners until he was finally placed in a shrine. However, (surprise) Koudeki of the Honami Clan of sword polishers and connoisseurs got enchanted by his beauty and took him from the shrine.
The Honami Clan gave Tsurumaru to the Date Clan of Sendai Domain (1716), who later presented Tsurumaru to the Meiji Emperor (1901), and he remains in the Imperial Collection to this day, alongside Ichigo Hitofuri, Uguisumaru and Hirano Toushirou.
Tsurumaru keeps talking about him looking like a crane in some of lines. This is because his name (鶴丸) is written with the Kanji for crane (鶴). The crane was also the crest of Mori Yoshinari (Odagumi period).
Although Tsurumaru's symbol (crane) is a traditional sign of fortune and longevity, he brought the opposite to his chain of masters.
Tsurumaru says that he hates boredom and always seeks for surprises to while away his endless longevity, being the best preserved blade from the Heian period despite his turbulent history.
Gojou (the swordsmith Tsurumaru was forged by) is said to be the disciple of Sanjou Munechika, Gojou Kanenaga, which makes Tsurumaru seem like the grandnephew to the Sanjou swords. Maybe his and Mikazuki Munechika's ways once crossed in the past.
Some fanworks depict Tsurumaru with Ookurikara and Shokudaikiri Mitsutada. This is due to Mitsutada, having been owned by Date Masamune while Ookurikara is speculated to have been a sword of Date Masamune's, or his son Date Tadamune. Together, these three TouDan (+ recently released Taikogane Sadamune) are known as the Dategumi for having been at the service of the Date Clan of Sendai Domain, although at different times in History.