Darosio was encountered during the search for the the Rainbow Knights. He was gathering memory-orbs of the Azure Knight as a part of her trial; he gathered four, which Tamiel Hymnspeaker managed to steal, before joining forces with the party to retrieve the final, fifth one. This occurred during the quest A Rainbow Connection, on a smaller island upon the Lake of the Tanglelight Forest.
Darosio used to belong to the Briarborn tribe of Centaurs, and he used to be a Centaur too, before a Neznámy Priest of fell gods, and his gaggle of Sea Hags and Kelpies, defeated and cursed him, turning him into a Nuckelavee, a type of Fey. He was unaware of his fate, until the party managed to prove it to him, which caused a lot of distress.
He was ready to accept his death and dissolve in the waters of the Lake, which hurt him, but Tamiel convinced him to keep fighting and look for a cure. The last time Darosio was seen, he was heading towards Eleutheria, because the Azure Knight revealed that Lord Attys possesses the means of reversing Darosio's condition.