Get really familiar with what it is you want to do and with companies that do what it is you’re trying to do.
If you’re shooting for a novel do a novel. If you’re trying to make a comic of some sort it should probably already be in the correct format for the intended medium. I’m not entirely sure what you mean by “anime/manga related” but to be frank, if you’re trying to do a manga you will have a bit more trouble. There isn’t a ton of space for non-Japanese manga because it is a LOT cheaper to just license one of the thousands of pre-existing titles and hire a translator, an editor, typesetter, etc than it is to pay for new work to be created from the ground up. And its a giant well of reliably professional-looking work that’s already there. But anime-inspired styles are pretty popular right now!
A lot of agents hang out and query on Twitter. Look at the bios of creators who you feel do work comparable to yours and see if they’re agented. Look at those agents and the agencies they work with. Don’t email them unless you know they’re querying. Cast the widest net possible within reason (you’re not gonna want to approach an agent that mostly handles non fic for something like what you’re describing) be patient! Ask for input!
