Ossia Island is a city on a lake in central Urobos. Each night, the skies are filled with incredible displays of festive fireworks. These are crafted by Ashley, the Fire type Gym Leader and host of the 6th gym.
Ossia is a musical term for an alternative passage which may be played instead of the original passage. The original Italian word means "or rather", and is itself derived from the Latin o sia, meaning "or be it". This follows the theme of locations in Urobos being named with musical terms, and may relate to Ossia Island serving as an alternate path the player can take through the region rather than the long route taken earlier in the journey.