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The dates
His earliest dated blade is a two-character tachi of 1278 (Kōan 1), and the latest, a tachi signed 来源国俊作 (Rai Minamoto Kunitoshi saku) of 1321 (Gen'ō 3); both are in the Tokyo National Museum. Neither his year of birth nor that of his death is on record. The signatures 来源国俊 (Rai Minamoto Kunitoshi) and 源来国俊 (Minamoto Rai Kunitoshi) suggest that the family surname was Minamoto (源, Minamoto).
The tachi of his 75th year
A tachi in the Tokugawa Art Museum, an Important Cultural Property since 1954, is signed 来国俊 正和二二年十月廿三日 (Rai Kunitoshi, Shōwa yonen jūgatsu nijūsan-nichi), followed by two illegible characters and by 歳七十五 (sai shichijūgo), “75 years”. The official database of designated properties reads the year as Shōwa 4 (1315), with the 四 (shi, “four”) written as 二二 (ni ni, “two two”), and explains that the two illegible characters may belong to the swordsmith or to the client. If the 75 years are the swordsmith’s, he was born around 1240 (Ninji 1), as Sesko deduces.
The date differs according to the source: Shōwa 4 (1315) for the official database and Sesko; Shōō 2 (1289) for the Nipponica encyclopaedia and the Nihon Kokugo Daijiten (日本国語大辞典, Nihon Kokugo Daijiten); Shōwa 5 (1316) in the text of the Bunka Isan Online record of the Nezu Museum tachi. The Atsuta tantō, of 1316 (Shōwa 5), is for the official explanation the work of the swordsmith at the age of 76, which fits with 1315.
One swordsmith or two
The oldest sword books, from 1381 to 1483, list a single Kunitoshi. From the end of the Muromachi two appear, “Niji Kunitoshi” and “Rai Kunitoshi”, and the Kotō Meizukushi Taizen, of the 18th century, makes them father and son: the Niji, born in 1240 and died in 1344 at the age of 105, and the Rai, born in 1299 and died in 1339, unreliable data. Today most scholars, such as Honma Junji, who formerly argued for two, and Tanobe Michihiro, think of a single swordsmith whose style changed over the years. The Hon'ami house distinguished in its certificates between 二字国俊 (Niji Kunitoshi) and 来国俊 (Rai Kunitoshi), and the Japanese Wikipedia considers the two-person thesis more likely. The Agency for Cultural Affairs itself is not consistent: in the record of the Kurokawa Institute tantō it speaks of Rai Kunitoshi as “son of Niji Kunitoshi”, and in that of the tachi of his 75th year, of a single master of the school.
The “Rai” signature
The first signatures with 来 (Rai) are a tantō of 1289 (Shōō 2) and a tachi of 1290 (Shōō 3), when the swordsmith was around 50: that is why there are so many two-character pieces. Sesko thinks that he took the family name when his father retired or died. He sees in him the “twin brother” of Osafune Nagamitsu: dates from 1279 to 1321 against 1274 to 1320, both sons of a founder, and with a style that moves from showy to calm.
Sons and workshop
Tradition gives him as sons, in this order, Ryōkai (了戒, Ryōkai), Kunimitsu (国光, Kunimitsu), Kunizane, Tomokuni and a second 国歳 (Kunitoshi); some add Kuniyasu. Rai Kunitsugu (来国次, Rai Kunitsugu) would be his son-in-law or Kunimitsu’s elder cousin. The dated blades of his last years, when he was already 79 to 82, were signed by the workshop in his name: Sesko gives to Kunitsugu those with a certain stroke of the character 国 (kuni) and to Kunimitsu those of Gen'ō and Genkō. In the Chūshin Mono (注進物, Chūshin Mono), the 1313 report on cutting swords commissioned by the bakufu, with 60 swordsmiths, Ryōkai appears but Kunitoshi does not.