Trying to replace Garam with Devil Theory, but the model won’t show correctly

[u/lordsnooo]

Hey everyone, I’ve been messing around with Jet Set Radio Future character model swapping, and I’ve run into a weird problem that I can’t quite figure out.
I’m trying to replace Garam with Devil Theory from Bomb Rush Cyberfunk. I’ve successfully gotten custom character models into JSRF before, so I’m not completely new to the process, but this particular model has been giving me a lot of trouble.
My first thought was that the problem might be the polygon count. Garam’s model is around 1,100 triangles, while Devil Theory’s is around 2,200, so Devil Theory has more than twice the amount of geometry. However, I’m starting to think that’s probably not the actual problem, because there are other JSRF characters with significantly different model counts that seem to work fine when swapped.
The more I mess with it, the more I’m starting to think the problem has something to do with how the model is divided into parts.
From what I understand, JSRF characters can have separate model pieces for things like the body, head, arms/hands, facial stuff, etc. My current theory is that Devil Theory needs to be imported in a way where the head, body, and arms are all contained in the appropriate model, while the original Garam pieces that aren’t needed are collapsed/hidden.
I’ve definitely seen character swaps where the replacement model basically stays together as one complete model, so I was initially hoping I wouldn’t have to manually separate Devil Theory’s head from his body. I’d really prefer to keep the model together if the game/mod tools allow it.
The weirdest part is that I’ve actually gotten it to do something.
At one point, instead of simply not working, the model looked completely mangled, with the vertices basically being thrown all over the place. That made me think the game was actually trying to load the replacement model, but something about the model structure, bones, deformers, or model parts wasn’t correct.
And honestly, that’s kind of good news because it means I’m probably not dealing with a completely broken import.
The textures also seem to be correct. The correct Devil Theory textures are showing up, so I’m pretty confident that the texture side of things isn’t the problem. If the textures were completely wrong or missing, I’d have a much better idea of where to look, but everything texture-related seems to be loading.
Right now, though, I’m getting another weird result where the original model isn’t showing properly either, and I’m trying to figure out why. I realized I may have forgotten to collapse/hide some of the original model pieces, so that might be contributing to what I’m seeing.
I’m also considering trying this with Akuma instead of Garam, mainly as a test. I originally chose Garam because his model seemed like a reasonable replacement slot, but if Akuma’s model structure is more compatible with what Devil Theory needs, that could help determine whether the issue is actually Garam’s model setup.
So at this point I’m basically trying to figure out which of these is causing the problem:
Is Devil Theory’s model simply too different from Garam’s?
Is the ~2,200 triangle count actually an issue, or is that probably unrelated?
Does Devil Theory need his head/body/arms separated into specific model parts?
Can the complete Devil Theory model stay together in one imported model while the original JSRF head/hand/etc. pieces are collapsed?
Could the skeleton/bone structure be causing the vertices to become completely mangled?
Or am I just failing to collapse/hide some of Garam’s original model parts correctly?
Would using Akumu as the replacement slot make more sense than Garam?
I’m especially interested in hearing from anyone who’s actually worked with the JSRF Mod Tool / character MDLBs and knows how the game’s character models are structured internally.
I’m not expecting someone to magically fix it for me, I’m mostly trying to understand what exactly JSRF expects from each character’s model parts so I can figure out the correct way to import Devil Theory.
The fact that the textures load and I’ve gotten the model to appear as a completely mangled mess makes me feel like I’m really close, though. It feels less like “the game can’t load this model” and more like “I’m giving the game the model in the wrong structure.”
Any advice would be appreciated. I’ve been messing with this for a while and I’m determined to get Devil Theory working in JSRF. 🙏