Agent 8 did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Agent 8, codenamed Number 10,080, is a playable Octoling character from Splatoon 2: Octo Expansion. They have suffered from amnesia and was found by Cap'n Cuttlefish at the Deepsea Metro. In the Octo Expansion, Agent 8 will have to do various missions with the help of Cuttlefish, as well as Pearl, Marina and Agent 3.
Agent 8 can show Mem Cakes to a character named Iso Padre in order to regain their memory.