The story
- Japanese · borrowed from姉妹丼“lit. older sister [and] younger sister donburi”
- English todayshimaidon
From Japanese 姉妹丼 (shimaidon, “lit. older sister [and] younger sister donburi”). Compare oyakodon (“a threesome with the mother of one's partner”).
Etymology from Wiktionary, CC BY-SA 4.0.