doraemon darake
ドラえもんだらけ (Doraemon Darake, "Full of Doraemon")
A famous episode from volume 5 of Doraemon manga, which involves the titular character bringing four instances of his future self to help him doing the homework for Nobi Nobita, only for it to ended up with him being beaten up by his future selves.
This episode is notable for displaying the concept of time paradox, as the beaten-up Doraemon would be then brought back into the past by his past self every two hours while he's trying to rest, gradually increase his frustration and resulting into the "8-hour" Doraemon (the fourth copy of future Doraemon bought from 8 hours into the future) beating up his past counterpart.