Training
- He was born in 1950 (Shōwa 25) and lived in Shimohonjō, in Saikawa-machi (today Miyako-machi), in Fukuoka Prefecture.
- He learned first from his father, the swordsmith 國光 (Kunimitsu), who signed 豊前住河野国光 (Buzen-jū Kōno Kunimitsu) and called himself 左国光 (Sa Kunimitsu). In those years the son signed as the second of that name: 左国光二代 (Sa Kunimitsu nidai).
- In 1975 (Shōwa 50) he became a pupil of the Living National Treasure 月山貞一 (Gassan Sadakazu) to learn forging and engraving (彫物, horimono). The master gave him the character 貞 (sada), and from then on he signed 貞光 (Sadamitsu).
With his father
There are blades with the signature of both, 豊前住河野貞光国光作 (Buzen-jū Kōno Sadamitsu Kunimitsu saku). In those years, with his father ill, much of the work that bears the name of Kunimitsu was made by Sadamitsu.
The “Kotetsu of today”
Among the pupils of Gassan Sadakazu he is held to be one of the most skilled, and for the cutting of his blades, the first among the swordsmiths of his time: hence the name 今虎徹 (Ima Kotetsu), “the Kotetsu of today”. Blades of his have been tested cutting thick bamboo.
Competitions
- He won the 努力賞 (Doryokushō) many times, and other prizes at the NBTHK 新作名刀展 (Shinsaku Meitōten). The years are not given.
- He does not appear in the NBTHK catalogues or prize-winner lists consulted, from 2017 to 2026, nor as a mukansa. Those of earlier years could not be consulted.
His death
He has died: so say the descriptions of his blades. The date has not been found in any reliable source.