Yamakoshi was Lanny's talking pet fish. He and Lanny usually plot together to get rid of Brady and Boomer and make Lanny the King Of Kinkow. He was once the twin of the first king of Kinkow, but he was turned into a fish, and becomes human when he is in his castle on the dark side.
He is the main antagonist of Pair of Kings, until his defeat at the end of season 2.
Yamakoshi is perpetually grumpy, and, despite being his best and only friend, he and Lanny are always insulting each other.
Lanny appeared to receive him when he was a baby. He is 100 years old. (No Kings Allowed)
It seems that he is the true schemer against the kings, though Lanny is the one who carries out the plans. Only Lanny seems to understand Yamakoshi when he speaks, as Brady and Boomer only heard bubbles. (No Kings Allowed, The Evil King)
Kalakai (Yamakoshi's human name) and his twin Malakai were the first rulers of Kinkow. Kalakai began to grow drunk with power, and he turned evil. He turned on his brother, and fled The Castle after losing in a sword fight with his brother. He then created an evil castle, and started the Dark Side. Malakai captured him, and managed to turn him into a fish. He was then given to Lanny as a gift. (The Evil King)
The kings were asked to steal Yamakoshi in order to join the Riptides, a group of kids who pulled pranks all over the island. When the kings stole him, Lanny got upset, causing the kings to return Yamakoshi instead of joining the Riptides. (No Kings Allowed)
He and Lanny got the kings thinking about who is the older king and they plan that if they find out, then the older brother will become king and Lanny will have only one king left to take down. (Journey to the Center of Mt. Spew)
Lanny becomes king. Zadoc kidnaps him to kill him and rule Kinkow. Yamakoshi escapes through the toilet and tries to save Lanny. He finds the Boomer and Brady. He tries to talk to them but they don't understand him, and hear bubbles. (Kings of Legend)
He later suggested Lanny break the bottle holding the cure needed to cure Mikayla so that Brady would face off, and probably die, againt the Waka Waka Bug's Queen in an attempt to get the cure. (Big Mama Waka)
After the occurring of the twin moons, he transformed into his human form when Lanny placed him on his throne. Desperate to gain the rings, he sent Lanny to stab Brady with an enchanted thorn, thus turning him evil. However, Mikayla managed to free Brady with a kiss while Mason distracted Kalakai. Kalakai managed to gain the rings, but as Boomer and Brady are the kings, they were able to call the rings to themselves. Using them, they combated his magic staff and defeated him. He was knocked out of his castle, which turned him back into a fish. Lanny later found him and continued to keep him as a pet. (The Evil King)
- Yamakoshi was set up as the secret main antagonist of the series in Season One.
- Yamakoshi revealed himself as the main antagonist in Season Two, and was defeated by the kings in the Season Finale.
- Though Yamakoshi said he would continue to plot to kill the kings, he never made an appearance in Season Three, which was the last season.
- Yamakoshi was with Lanny ever since he was a baby and was brought at Fishy U Love.
- Yamakoshi wanted a suprise 100th birthday.
- Only Lanny can understand Yamakoshi other people will hear glubing sounds not even the kings can understand him.
- Everyone thinks he is a frog or a messed up crocadille.
- Even though they both annoy each other Yamakoshi deeply cares about his safety as he flushed himself down a toliet and warned the kings (though they didn't know what he was saying and the parrot bird helped)
- Yamakoshi is Lanny's only best friend.
- He came back to live with Lanny after he was defeated and transformed back into a fat ugly fish.