Hyuponia, the Kingdom of Sorrow, is hidden deep under the Sea of Tears. There are many tall buildings, and a large palace suspended in the air, presumably the residence of the King of Sorrow. There is also an area called the Forgotten Path, which is located in a mysterious, shadowy void of the kingdom and leads up to the King's palace, the Terminus of Tears.
No inhabitants live in this kingdom, except the King of Sorrow.
Although Klonoa and friends were able to destroy the Ishras Ark, they failed to stop it from opening a path to the Kingdom of Sorrow. They entered the Kingdom and wondered if they were too late, but Leorina informed them that they could still prevent sorrow from consuming the world if they defeat the King of Sorrow. Klonoa, Lolo, Popka journeyed through the Kingdom and eventually reach the Forgotten Path, which took them up to the King of Sorrow's residence, the Terminus of Tears. The King of Sorrow revealed to them the details of his plan to bring sorrow back to Lunatea. He loses his remaining sanity, deciding to take out his pent-up anger against Lunatea on Klonoa. He attacks Klonoa, who deflected his first attack. He collapsed and began lamenting that there was no place for sorrow in the world.
Leorina arrived and reprimanded the King for thinking he's the only one who was sad. She gave Klonoa the Elements from the other four kingdoms, giving him the power he needed to defeat the King. The King suffered a mental breakdown, isolating himself in a forcefield and attacking Klonoa again, ultimately being beaten. Defeated, he begged Klonoa to help him. Klonoa agreed, and rang the Bell of Sorrow, restoring the power of sorrow. As the King laid dying in his arms, Klonoa reassured him that he no longer has to be afraid, and that sorrow would not be forgotten again. The King was finally able to be at peace, and evaporated in Klonoa's arms. The people of Lunatea helped rebuild the Kingdom of Sorrow, with Leorina at the head of the effort.
- Traces of various music from Door to Phantomile can be heard throughout the soundtrack of the level in the Kingdom of Sorrow, "Lolo", "Granpa's Theme", "Windmill Song", and the "Song of Rebirth" are four of the songs briefly heard in the music. 
- If the music to this level is played backwards, the theme of cursed Leorina can be heard.
- Hyuponia may be named after Huepow, the a character from Door to Phantomile.
- It is possible the King of Sorrow doesn't die, but is, in fact, the element itself, as the cutscene shows the king disappearing and the element in its stead.
|Sea of Tears|
|Dark Sea of Tears - Empty Sea of Tears|
|Claire Moa Temple - Noxious La-Lakoosha|
|Joilant Plaza - Jungle Slider - Joilant Fun Park|
|Volk City - Underground Factory - Volk Hall|
|Embryo Compass - The Ark Revisited|
|Mountains of Mira-Mira - Maze of Memories - Indecision Pass|
|Kingdom of Sorrow - The Forgotten Path - Terminus of Tears|
|Klonoa - Lolo - Popka - Leorina - Tat - Momett - The High Priestess - Baguji the Wise - King of Sorrow|
|Momett Dolls - Dreamstones - Elements|