The name of extra diff obeys the rules. It's anime char names, not usernames (unless if any of same spelling, byte per byte).
Personally, ppl may complaining on it because "vs" is used for duels, not for marriage nor concubineship. To me, personally, would change the "vs" to "+". Unless Chloe minded an erotic duel ending with the two...glued on each other. Like Mr. and Ms. Smith (that Brad Pitt and Angelina Jolie movie).
I also feel the extra is a bit overmapped. I should reach A in HT, but got just a C. This diff needs a deeper analysis imho.