Taiwan/Vietnam is a common pairing involving the characters Taiwan and Vietnam. It is also known as TaiViet and Lotus and Plum (due to Taiwan having a lotus in her hair and Vietnam due to plums growing in both Vietnam and Taiwan).
The ship came from the web comic where Taiwan and Vietnam first interact. Taiwan starts by thinking that Vietnam is a "cutie" and that she has an embarrassing picture of her, which Vietnam proceeds to blush but is dragged by Taiwan towards the Photo Studios, which their eyes were made bigger. Blushing at the picture, it ends where Vietnam glares at the picture in awe thinking it was her and it was said by Taiwan that everyone made her stay there, indicating that Vietnam wanted to leave. However, it was shown that their eyes were enlargened which made it "cute".
Outside of the webcomic, the ship is usually portrayed as Taiwan being the cheerful one, and Vietnam being the rather quiet and serious one. Similar to America/Belarus, the two are opposites. However unlike Belarus, Vietnam doesn't take any approaches to murder Taiwan, nor get angry at her, and usually ends with her in blushing or embarrassed by Taiwan's antics. However, fans believe deep down, that Vietnam actually doesn't mind this at all. The fandom also believes that Taiwan might actually have a crush on Vietnam due to how close she usually is to her, and how the fact that she thinks shes "kawaii" out of everyone else. Many fans think that it's an illusion that it's one sided and it's actually, in reality, two-sided, but believes Vietnam refuses to admit it.