All right, this is just a small drabble I'm writing in regards to something I realized from the 'World God Only Knows' franchise, that I don't remember being explained. (Also I've only read the manga so far so sorry if an explanation is already there.)
After Keima conquered any of the girls, she would forget all about him; however, what about the third party?
Most captures were in private, but some were very unsubtle; I'm looking at you Hinoki.
However, the people to look at most are Ayumi and Chihiro.
The two are best friends; talk all the time on pretty much anything.
So if the third party retained their memories, Chihiro would have confronted Keima and Ayumi on why they acted like strangers.
New hell was in a crisis; they could not go around wiping memories carefully. The manga shows their memory wipes aren't perfect, so why does Keima remember?
My theory is simple; the collar. All demons and buddies are given the collar when they make a contract, and while the threat of decapitation is great, there are a myriad of less noticeable methods to kill someone who breaks a contract.
My belief is that with each loose soul captured, new hell simply launches a mass memory wipe to anyone the slightest bit involved; however, to ensure efficiency amongst the capture squad, the collars act as a barrier to protect the wearer.
Mind you, that this is a simple theory I thought of while reading 'Those Mindnumbingly Boring Days', by 'Sir sleeps-a-lot' (Some names on this site are quite unique; Max approved); so give me your thoughts in the reviews.
This was PheonexX's very own Max Azure bolting out of here; peace out.