desu

The story

1. Japanese · borrowed fromです“be”
2. English todaydesu

Borrowed from Japanese です (desu, “be”), the polite form of the Japanese copula, found most often at the end of a sentence. Know Your Meme attributes its spread to 4chan memes of the Rozen Maiden character Suiseiseki who ends every sentence with desu (see also キャラ語尾).