For Jujutsu Shenanigans , the JJK characters that are not in the game are mostly the ones outside its 19-fighter roster, while the guide specifically confirms the game does include characters like Megumi, Mahito, Gojo, and Sukuna.

What’s confirmed

The roster guide says Jujutsu Shenanigans has 19 fighters total.
A tier-list guide also specifically mentions Megumi, Mahito, Gojo, and Sukuna as playable styles.

Likely missing JJK characters

Based on that limited roster, characters commonly not included are:

  • Yuji Itadori if you mean the full anime/manga cast and not a specific move-set variant.
  • Nobara Kugisaki.
  • Yuta Okkotsu.
  • Maki Zenin.
  • Toge Inumaki.
  • Nanami Kento.
  • Todo Aoi.
  • Jogo.
  • Hanami.
  • Choso.

Quick note

Because the roster can change with updates and custom movesets, the safest answer is that only the 19 listed fighters are confirmed in the game right now , and anything beyond that is not part of the core roster.

TL;DR: The game has a limited roster, so many major JJK characters are not in it yet, including Nobara, Yuta, Maki, Inumaki, Nanami, Todo, Jogo, Hanami, and Choso.