Since the mid Edo period, Seppuku was simplified and ritualized, eventually reduced to a so-called Sensu-bara pattern, in which an assistant swung the sword down onto the person committing Seppuku the very moment he reached for Sensu (a fan) which represented a short sword or Wakizashi used for disemboweling.
江戸時代中期以降になると切腹自体が簡略・儀礼化し、いわゆる「扇子腹」の形式で行われるようになり、切腹人が小刀・脇差に見立てた扇子に手を伸ばそうとした瞬間に介錯することがほとんどであった。