This is also a list of all third party IPs that have at least one game that sold more than 1 million copies in Japan. I put them in order taking into account their best-selling game. Also, I will discard any sports/racing game or IPs whose origin are not from a videogame.
1) Monster Hunter (MH Freedom 3, PSP, 2010, Capcom, 5.3 millions)
2) Dragon Quest (DQ IX, NDS, 2009, Square-Enix, 4.4 millions)
3) Final Fantasy (FF VII, PS1, 1997, Square-Enix, 4.1 millions)
4) Yokai-Watch (YW2, N3DS, 2014, Level-5, 3.3 millions)
5) Street Fighter (SFII, SNES, 1991, Capcom, 2.9 millions)
6) Minecraft (MC: Switch, Switch, 2017, Microsoft, 2.8 million* probably more)
7) Resident Evil (RE2, PS1, 1998, Capcom, 2.55 millions)
8) Chrono (CTrigger, SNES, 1995, Square-Enix, 2.03 millions)
9) Puyo Puyo (Super PP, SNES, 1993, SEGA, 1.7 millions)
10) Kingdom Hearts (KH2, PS2, 2005, Square-Enix, 1.6 millions)
11) Crash Bandicoot (CB3, PS1, 1998, Activision, 1.5 millions)
12) Mana (SoM, SNES, 1993, Square-Enix, 1.5 millions)
13) Tamagotchi (Tama 2, GB, 1997, Bandai-Namco, 1.45 millions)
14) Tekken (T3, PS1, 1998, Bandai-Namco, 1.40 millions)
15) Virtua Fighter (VF2, Saturn, 1995, SEGA, 1.3 millions)
16) Lode Runner (LR, NES, 1984, Konami, 1.1 millions)
17) Onimusha (O2, PS2, 2002, Capcom, 1.1 millions)
18) SaGa (SaGa, GB, 1989, Square-Enix, 1.1 millions)
19) Warriors (SW, PS2, 2004, Koei-Tecmo, 1.07 millions)
20) Parasite Eve (PE, PS1, 1998, Square-Enix, 1,06 millions)
21) Professor Layton (PL, NDS, 2007, Level-5, 1.01 millions)
22) Gradius (Gradius, NES, 1986, Konami, 1.00
million)
23) Star Soldier (SS, NES, 1986, Konami, 1.00 million)
24) Metal Gear (MG4, PS3, 2008, Konami, 1.00 million)
If Level-5 aren’t near bankruptcy, Yokai-Watch could be a good candidate.
Would be a bit surprise if we won’t get at least a YW or Puyo Puyo mii costume. Chrono was rumoured to be a candidate for playable fighter (as per seven square leak) and this list makes sense.
But honestly anything can happen.