i am absolutely answer choice C right now - momo is my favorite character in the series, and she looks absolutely gorgeous in her introduction! who cares about romance? i only care about feisty redheads!
cheng mo's username is actually something i had a lot of trouble with - it's 朱砂点墨 *zhu sha dian mo*. the last bit is, of course, a pun on her own name - 墨 means ink, but it's also the same *mo* that's in her name.
朱砂 means cinnabar or vermilion; 点墨 is a verb meaning 'to dip into ink,' and it's often used as metonymy for the act of writing or editing. in other words, she's an editor who uses red ink. but quite frankly, that doesn't make a good username - so i decided to defer to rule of cool and translate it more literally as 'cinnabar ink.'
the rest of the YG gang are much more straightforward, lol. ah tai's username is literally just his initials (AT).
yuncheng is a little more complicated - 允诚 *yuncheng* means 'sincere' or 'honest,' but it's also a common actual name. i considered translating it as 'sincere' for a while, but one of the S2 chapters actually confirms it's his legal name.