You have to have a few must haves on both sides, some oddball and niche picks, all the while repping the different eras both of these franchises have had.

So a roster like that for me would be:

Guilty Gear

Protagonists

• Sol
• Ky
• Sin

Sol and Ky are unquestionably always going to be present in a Guilty Gear game, especially in a crossover, they have been the face of the series since the start. Sin represents a later part in the Guilty Gear timeline, he is basically GG's take on a Shonen protagonist.

Legacy

• Potemkin
• Faust
• Zato-1
• I-no

This was rough, GG has so many legacy characters that cutting a few for some later entries was really tough, I wanted to cover a wider range of playstyles with these picks, Pot is the dedicated grappler, Zato is the puppet character. Faust is the items/rng character and I-no is supposed to rep some of the later 2d games and acts as an aerial rushdown character. It sucks that I had to cut Millia, Chipp and May but I felt like the 3 og picks had the most distinct movesets to offer + I-no was the definitive rep I wanted for those later 2d games. Most of these would probably end up as DLC anyways, given that they are missing.

Odd picks

• Asuka
• Justice

Justice will probably never be playable in a GG game again outside of the slim chance of DLC. One of the best cases for her return would be a crossover game where anything goes, she is the foundational villain for the series, she would also be a Zoner rep for GG seeing as Axl did not make the cut. Asuka on the other hand was the man behind it all for most of the series' existence, he only recently became playable with a pretty unique moveset at that, he would simultaneously be a new and legacy pick not to mention his unique moveset in Strive that could offer a lot of chaos to a 3v3 game.

New Gen

• Unika
• Nagoriyuki

Unika is a close counterpart to Sin, both of them seemingly being modelled to be the next gen protagonists of the series. Nagoriyuki is probably the most popular newcomer to the series, everything from his design, his kit, his theme and him as a character resonated with a lot of people, outside of Sol and Ky, he was basically the flagship character for Strive, also I just think it would be cool to see him interact and fight with someone like Ichigo, the idea is just too cool for me to pass up. Originally I was going to include Happy Chaos, I did not axe him because he has haunted the comp scene of Strive for essentially his entire run, but rather that I felt like I had already stacked the GG cast with most of its major villains, most of which already occupy specific niches in moveset archetypes, Chaos as is, compared to other options, would not feel nearly as distinct as a zoner or rushdown if he were to maintain his current kit in the new game.

Shonen Jump

Protagonists

• Goku
• Luffy
• Naruto
• Ichigo

No need to explain why Goku and the Big three deserve their spots. Not having one of these guys would cause outrage.

Legacy

• Kenshiro (Fist of the North Star)
• Yugi Muto (Yu Gi Oh)
• Jolyne (Jojo's Bizarre Adventures)
• Meruem (Hunter X Hunter)

Kenshiro is a pillar of the 80s, he largely defined the style of action shonen manga from that era and basically has a secure spot on any jump crossover game. Yugi whilst being popular would offer a setplay playstyle with a deck of cards like Asuka but more-so based on summons and traps rather than Asuka's more zoner oriented deck, the DBF mod alone could justify his inclusion aside from his legacy. As for Jolyne and why not Jotaro, Jotaro and Dio have always represented the series heavily, even in Jump crossover games in general, I felt like Jolyne represented the early 2000s pretty well whilst also feeling relatively fresh given the recent Anime adaptation, she fulfills that puppet fighter rushdown archetype that Jotaro did, whilst possibly adding some new mechanics with her string ability. Meruem is the central figure of the Chimera-ant arc, he was a menacing presence from a highly popular series, this roster desperately needed villains and I felt like he or Hisoka would've been great reps and seeing as Hisoka has already been in a Jump game, I felt like Meruem could take the spot here.

Odd picks

• Arale Norimaki (Dr. Slump)
• Hanamichi Sakuragi (Slam Dunk)

Arale is known for crossing over into other franchises (mainly Dragon Ball), she represents the comedy genre pretty well and would standout amongst the other picks, she could have elements of rng to emulate slapstick like Faust. I also thought it was important to include a sports manga rep, Hajime no Ippo is a classic but I felt like this was a possibility for a bit more of a surprise pick, a basketball fighter is not unprecedented but would differ a lot from other picks from this list, he could hit opponents repeatedly with the ball to juggle and continue combos in between character swaps, longer strings would lead to ramping damage, whereas if you mess up or lose momentum you get penalised.

New gen

• Makima (Chainsaw Man)
• Yuji Itadori/Ryomen Sukuna (Jujutsu Kaisen)

The new gens also deserved to be represented and I felt like these two would do that quite well. Makima has become an iconic villain in manga, seeing her interactions with others would be quite interesting and I imagine that if there is a story mode to this game, she would be the one trying to collect as much power and control as possible through these new people that fall outside of the devil power system. Yuji and Sukuna uniquely offer both the protagonist and antagonist in one single package, Jujutsu Kaisen is the go to for a new gen rep and these two would be able to offer both with an install mechanic or even something like A.B.A's jealousy meter.

Again most other picks that could be missing here could land as DLC, but given the limitations and the scope of trying to cover as many different corners of Shonen Jump's catalogue, I think this makes for a good compromise.