The Ninja Fish is a Siamese Fighting Fish with a golden sword, which is given from his master.
When Jocktopus punched Milo really hard, Milo flew out of the tank, and ended up in a glass bowl. He hears cheering and screaming coming from the bowl next to him, and sees the ninja fish fighting another ninja. After the ninja fish defeated the other ninja, he jumped to his bowl. Milo complements him with his fighting skills. He then asks if he can touch his sword. But the ninja fish thought he will "shame it with his touch", and that he already lives with enough shame. Milo wanted to know why his life is shameful, so the ninja told him the sword was given from his master to protect the weak, and avenge injustice, but the ninja only uses the sword for money and sport. He refers to himself as "pitiful". Milo tells the ninja is not pitiful, but lucky to have met him, since he and the ninja can bring peace to Freshwater High. At Freshwater High, Jocktopus was bullying and making fun of Albert, so Milo and the ninja came. Milo at first gave Jocktopus a warning and to walk away, but Jocktopus refused to, and decided to defeat the ninja. However, the ninja blocked all Jocktopuses attacks with his sword, which damaged Jocktopus's arms. Then the ninja, under Milo's orders, puts Jocktopus in a glass bowl. Milo later became too lawful, and with the ninja's help, he trapped everyone in glass bowls. Later, Oscar climbs the shelf the bowls are in too free everyone, but Milo tried to stop him. Unable to stop Oscar, he called the ninja to put Oscar in a bowl. Oscar then tells Milo that he's now a bigger bully than Jocktopus, making Milo realize his mistake, so he tells the ninja to give him his sword, so he could throw it out the shelf so the ninja could follow. After everyone was free, the ninja asked Oscar and Bea if they want to eat at the Hokey Poke ("Milo Gets a Ninja").