Itou Hachi does depict Rem with a lot less detail and "erotism" compared to the other two, so that mental age is really a turn off to our writer. I was thinking Rem won't get much panel time as a result...
Then Itou goes and makes Rem super excited about seeing a 7 year old in a skirt, so maybe Itou Hachi likes Rem well enough as a "comrade" and Rem's future isn't so bleak.