Sumitani's family ran a soy-sauce manufacturing business, but rather than entering the family trade, Masamine opted to study at Ritsumeikan University, with a view to becoming a swordsmith, graduating in 1941 with a degree in mechanical engineering.
He worked in the Bizen tradition, and was noted for his choji midare or "clove patterns" along the hamon of his blades.
[3] As well as swords, Sumitani also specialised in the forging of tosu knives and was a practitioner of bachiru.
[4] In 1975 he co-founded the Zen Nihon Toshokai ("Japanese Swordsmith's Association"), and served as the group's Vice-Secretary.
[3] He was given the status of mukansa, meaning that his work was no longer subject to judgement in competition.