Just had a thought. Who would make the ultimate 4 member team, able to clear all 30 floors with just the 4 of them? Discuss.
Here's my input. First you would need an excellent tank. I vote China because not only can she heal herself, she can cure a few crippling status effects.
You would also need a dedicated healer. I vote Reimu as she can heal the entire party, has a party wide DEF/MIND buff, and can cause PAR for clearing trash.
You would also need a damage dealer that also has good survivability. Pure glass cannons won't cut it for this team. Not sure who. Nitori maybe?
The last member could be a second tank, a pure supporter, or another damage dealer with good survivability.
Overall the whole team needs good survivability as they can't exactly switch for someone else. Oh and an ok focus recovery rate.
Discuss.
I may still be working on my first playthrough, but I don't see how you could effectively do this. Some bosses would simply run over you because you would not be able to do enough damage fast enough to beat them in the damage rush, effectively forcing you to overlevel to the point that the challenge loses some of its edge, so to speak. I think you could do the main game with only 4 characters with smart play and only a couple of extra levels, due to the lack of DEF/MND ignoring attacks. This is all in my opinion, though.
Other concerns:
Have to worry about resistances for EVERY party member. Would be hard to raise resistances much beyond normal playthrough levels because sharing SKP between 4 instead of 12 people is still less efficient due to the way the costs increase.
Best damage dealers are too fragile or have a glaring weakness that would be exploited.
Tougher damage dealers are too slow in output for the damage races.
Inability to Switch-nuke makes the races even harder.
Roadblock Bosses (off the top of my head, main game):
Flandre: Can you keep up with her damage output? Could you damage her before she killed you with Laevateinn?
Orin: Endurance. Can you keep up with the knights and her without getting worn out?
Yuugi: Would be able to OHKO everyone. No replacements would be killer.
These are just a few that come to mind here.
Still, would be interesting to try to see how far you can go. I know I've seen some people finish some absolutely ridiculous challenges in ADOM, for example (beating the game at LVL1, shield-throwing, eternium man... there are some crazy good people at that game)
If I HAD to try a team though, I'd definitely bring Reimu for group healing/buffing, and her PAR move to help make it through floors. You'd need two damage sources, one PHYS, one MAG...or a defenses ignoring attack. Perhaps Shikeiki? for Last Judgement + PAR for trash. Tanking... Meiling most likely, HP increasing like in Team Unappreciated for the defense ignoring boss attacks, and the extra healing + status healing for emergencies. 4th character is more difficult to decide.
Those are my thoughts on the matter. :V