Temtem

First, do the side quest to unlock the fishing rod. After that, go to Nuru Lodge in Kisiwa and check the weekly koish, you must find the perfect Koish (5/5) without delivering the 4/5 Koish, which makes it harder to find. It is fully depended on luck, but the fishing has a pity timer of 1000 (the 1000th Koish will be a perfect one), which may take you 4-6 hours to reach this number

Not confirmed, but if you miss the perfect Koish the pity timer might reset, so pay atention!

*Side quest for obtaining the fishing rod: * https://temtem.wiki.gg/wiki/Fishcraft