How long would it take to achieve this? I'm cosplaying as Kamina this January for a convention...

Sure.
Long as you get a good amount of volume, and are putting weight on the bar every few sessions you're good.
Oh and don't cut.

You can cut or you can build
Never both unless you're on drugs or you're a fat teen male or a pregnant/post pregnancy woman.

this user is right, cut or build. However, you can still follow the examples in with more food/more often to hit caloric surplus, just be eating healthy. No more cereal, more veggies, lots of protein.

More volume = more mass. if you're only hitting a group one day a week you either need to blast it that day or move it up to 2x/week

Thanks for the advice everyone! Gonna work my ass off to pull this off and hopefully reach Kamina status