On top of upgrading your characters the Amakumo Fruits are often used in Genshin Impact, while not that hard to find you'll still need a lot of them so here's a guide to where you can get your hands on a bunch.
Amakumo Fruits Location Genshin Impact
You will be able to find Amakumo Fruits on the Seirai island while getting electrocuted by the unending thunderstorm.
If you're looking for a more precise location for all these Onikabuto I'd advice checking the official interactive map where you'll be able to zoon as you see fit.
You can find the map on the Hoyolab website here.
