The Zenbei HARUKIYA origin theory: According to "Edo kaimono hitori annai" (the shopping guide of Edo) compiled in the same Bunsei era (1818-1829) as the above, Zenbei HARUKIYA, an eel restaurant owner received a large order for 'kabayaki' (eel split, grilled and basted with a sweet sauce) during the doyo, so he grilled eel on the day of the Rat, Ox and Tiger consecutively and kept it in earthenware pots;
春木屋善兵衛説-同じ文政年間（1818-1829）の『江戸買物独案内』によると、土用に大量の蒲焼の注文を受けた鰻屋、春木屋善兵衛が、子の日、丑の日、寅の日の3日間で作って土甕に入れて保存しておいた。