I never gotten to go to this extra bonus mode because of the requirements, but here is the answer (from gamefaqs)
Start Leon or claire, Normal mode.
-You cannot have more than three saves
-The game must be beaten within two and a half hours
-No first-aid can be used
-There can be no use of bonus weapons (Rocket Launcher, Gatling Gun, or Sub-Machine Gun)
Remember: The last qualification only applies to weapons you UNLOCK. You can still use the rocket launcher you get at the end and not have it decrease your rank. I think the same applies to the SMGs, but I can't speak from experience.
If your having a hard time with this, I would recommend using the infinite ammo cheat. That does NOT decrease your rank.
Do the same with claire B, hunk mode will be unlocked. You have to beat hunk mode to unlock tofu.