9S is the very special in the YoRHa army, and the only one male type character in NieR:Automata.If you are good at bullet hell, his special hacking skill will do a lot of help in your combat.9S is a lovely boy,
but he soon get mad after the 2Bs death.
Thats why I dont like him, this guy is too emotional, always being mad and do a lot of crazy things.
2B is not exactly B type, probably E type.In NieRs world, B for combat, E for assassination, her duty is not only for CQC, but to keep an eye on 9S, and kill him if he knows too much about the YoRHas top secret data.
In many country, such as china, japan, if you search 2B on the internet, you will find a very unusual result, the top of the list is always 2B lady. Why she is so popular? In my kind of view, Its all about Moe. Katana, Mini Skirt, and cute lady are fit for the otakus needs, just like Ayumi in X-Blades, Masako in the Buired Town2 etc.
From so far, there are still a lot of information that is still unknown to the players. I think Square Enix may publish the NieR2 or DLC in the near future, to help us know the truth of the NieR world. By the way, which one is your favorite android in game? A2, 2B or 9S?