In episode 56, this card is shown on Seeker's laptop when he was researching the Battle City participants and trying to figure out who should he duel first. This card is shown to be Mako Tsunami's rarest card.
In episode 69, Mako Tsunami uses this card during his Duel against Joey Wheeler. He summons this card via "Fortress Whale's Oath". This card then gained 200 ATK and DEF due to the effect of "Umi". This card attacks directly after "The Legendary Fisherman" attacks and destroys Joey's set "Rocket Warrior". On Mako's next turn, he uses this card to attack "Panther Warrior", but Joey activates "Magical Arm Shield" to redirect the attack to "The Legendary Fisherman", destroying it. On Mako's next turn, this card attacks "Panther Warrior", but Joey activates "Kunai with Chain" to equip it onto "Panther Warrior" and increase its ATK by 500. Joey then activates "Lightning Blade" to equip it onto "Panther Warrior" and increase its ATK by 800. "Panther Warrior" then destroys this card. After Joey won the duel, he obtained this card and "The Legendary Fisherman" from Mako as per the Battle City Rules.
Joey never played "Fortress Whale" in future duels. This is probably because he did not take Mako's "Fortress Whale's Oath" card.
In the anime, Mako Tsunami mentions that this was his most powerful card, which is ironic since in one of his previous turns, one of his "common" monsters "Amphibian Beast" had 50 more ATK, not to mention it was quite easier to summon than this card. This was probably said in order to add a more dramatic effect on the card.
In episode 74, this card appears within a series of flashbacks that show all of Joey's Duels in Battle City.
In episode 88, this card appears in a flashback Joey has when he mentally apologizes to Mako for letting "The Legendary Fisherman" be destroyed while being unable to save it from being destroyed.
In episode 124, this card is shown in a flashback that Joey has when he remembers all the Duelists he faced on his way to the Battle City Finals.