Having tracked part of an ancient song to somewhere off the coast, Kass downed a potion that would let him hold his breath far longer and dove into the water. He quickly sank onto his butt on the seabed, a side effect of the potion keeping him from being able to swim, so he begrudgingly walked on the bottom instead. The potion still fulfilled its intended purpose, at least; even 15 minutes later, Kass still didn't feel any need to breathe.
Close to another 13 minutes underwater, the bird came across a large gold-colored set of doors with several music notes engraved in them, and no obvious way to open them. Kass recognized this style right away; one would need to copy the notes on the doors to open them. Having left his accordion behind for fear of the water ruining it, he only had one option for getting by; he opened his beak, and sang out into the ocean depths.
It seemed like this brief song was intended to be sung underwater; his voice was surprisingly clear, and his exhaled bubbles almost seemed to harmonize with it. Some of said bubbles actually formed into the notes he was singing! Once he was done, he puffed his cheeks again and held his beak, nervous about letting out so much air when he couldn't swim. At this time, another side effect of the potion was making itself clear; his cheeks were far more elastic than normal, and without him even trying, they'd gotten nearly as big as his head!
Kass waited, hoping he'd sung right, and soon relaxed as he heard a rumbling sound. The doors slowly opened on their own, and he happily cheered, a large bubble leaving his beak before he stopped himself and held it shut again. Even with the potion's help, he was finally starting to feel some strain, the increasing effort of holding his breath making him blush. Still, he pressed on, not knowing if the potion might wear off if he went back to the surface.
Past the doors, the halls went on and on, the bird needing to hold his breath for nearly half an hour more before he finally came to his goal. A huge pedestal was ahead of him, and on top was a golden tablet; the song part he'd been looking for! Even with his cheeks and face turning purple, he climbed up to claim the tablet, then back down to search for his next prize: Air.
Now starting to struggle, Kass held his beak shut with his free hand as he made his way back outside. By the time he got there, he'd been underwater for well over an hour, and his cheeks were bigger than his head. He still had a long way to go to reach the surface again, still being unable to swim, and he started getting worried he wouldn't make it in time. With no other option, he just continued on, his lungs soon burning.
Even holding his beak didn't stop the bird from losing air in a constant trickle of bubbles, but with the surface getting closer, he wouldn't have to hold out much longer. As he approached it, though, he finally couldn't hold his breath any more; his beak opened wide and he exhaled all the air he had left in a huge bubble that was almost half as big as he was tall. Gurgling and just barely holding back from inhaling, Kass dashed the rest of the way to the surface and finally gasped after nearly 2 whole hours. That was way too close... But, it had been worth it; he was one step closer to fully learning the song he was looking for.