It was in one of his Famitsu column, give me a sec and I will find it.
Edit:
https://nintendoeverything.com/saku...ate-jokers-reveal-getting-some-rest-and-more/
"Nintendo had first approached me with a request: “We want you to reveal that Joker’s in development at The Game Awards 2018.” The timing wasn’t bad at all, it really was what made the flower that was
Ultimate’s release bloom. Of course, I hadn’t even started on development at that point, so there wasn’t any gameplay we could show off.
To that end, I thought that we could reveal him through an animated cutscene.
After seeing The Game Awards’ venue, I thought about how I could make the reveal interesting. I’d eventually reach the idea that Joker would infiltrate the venue and steal its “treasure” – an invitation to
Smash.
I’m familiar with
P5, so writing dialogue that suited the character wasn’t much of an issue. Scheduling with Joker’s voice actor – who’s quite popular – was a different story. We had fun recording the lines, though; the atmosphere in the recording studio was pretty cheerful. We only ended up with a few lines of dialogue, though… What a waste…
I’m not sure about whether or not we’ll do reveal movies for the other DLC fighters, but I’d like to do what I can (within the realm of possibility) to make sure you all enjoy them."