Wonder how many major Japanese devs/publishers have yet to have a playable character in Ultimate (well, besides Sony, but that's only because I'm pretty sure a Sony owned character is the least likely character to make it in given the issues between Nintendo and Sony)
Here's the list of major Japanese IPs, Developers, and Publishers that are not in Smash in any capacity right now. It's not necessarily a comprehensive list, but does lay out a number of options:
Koei Tecmo
Ninja Gaiden - Ryu Hayabusa
Dead or Alive
Dynasty Warriors
Arc System Works
Guilty Gear
Blazblue
River City
Grasshopper Manufacture/Suda 51
No More Heroes - Travis Touchdown
Level 5
Professor Layton
Yokai Watch
Bandai Namco
Tales
Tekken
Digimon
Dark Souls
Soulcalibur
Katamari
Capcom
Resident Evil
Monster Hunter
Devil May Cry
Phoenix Wright
(I'll just cut it off there, there's too damn much from Capcom that you could conceivably include).
Square Enix
Kingdom Hearts (sort of)
Crono
Mana
Nier
Tomb Raider (more of an acquisition, so I'm not sure she belongs here)
Konami
Silent Hill
Gradius
Sega
Puyo Puyo
Shin Megami Tensei (If Joker doesn't count as a rep, also technically another Atlus rep)
Shinobi
Yakuza
Phantasy Star
SNK
Samurai Showdown
Metal Slug
Sorry for the long list, but we could go incredibly deep into the pocket of Japanese franchises and not even touch Western IPs or half of these in the process haha.