How do I get the oni or that red skinned monster
You need to send surrogate women to the Orc camp, let them get impregnated (try to wait until all woman there are pregnant), and then raid them. Oni are just the Monmusu hybrid between Orc and a female slave.
You're right, massive brain fart on my end there. 6 looks to be effectively the 2nd item of clothing for a given creature, as sisters use 5 for their nun's habit and it's also used for goblins' arm bandages.
Checking it again, it's 7 that's new and is only used for the orcs. Even the Oni doesn't use it. It's also the same reddish-brown colour as the loincloth.
Also of interest is that the orc and goblin both have colour codes for their hair, despite not having any hair. I'd guess it's to do colour inheritance in the future as some kind of recessive gene, but maybe we will see monster variations like in MBM?
I changed the color for 7 and don't see any time it is used. Compared it to an original Orc before I switched the color, nothing, even in combat somehow. Maybe a variant/holdover they were playing around with or something they thought they changed but didn't. Maybe originally for something like cording for the necklace or fur for the boots? All supposition though.
Note while I edit this, but they still have data for Monster and Slave cages. Leftover from MBM porting or planned future feature, I don't know.
Also, considering how they've structured the data, I wouldn't be terribly surprised if they are aiming for a rudimentary faction/diplomacy system since sabotaging Monster camps(?) lowers infamy for yourself but sending breeding stock raises it. Could be a balancing act of preventing as much trouble as you can from sabotaging the Orc camps vs sending surrogates to raise or lower infamy in the various nations. And once they implement the gold system or other resources you can only really get by raiding (even if you don't want the women/monsters), combined with perhaps a request system and/or funding/supplying the monster black market? Probably a stronger incentive for everyone to play with the systems on offer.
Combine that balancing act with trying to get under a time limit for good endings and harsher aggro penalties/native infamy gain or something, and you might have a race to win against the nations closing in on you.