Manga by author Iwasaki Masakazu

Sakaine Douji is a loner and happy that way. But one day, a mysterious transfer student on her first day suddenly calls him out and, literally at sword point, declares him her boyfriend . It obvious she not... quite... right... A hilarious, slightly ecchi love-comedy ensues.

From MangaHelpers:The ruler of the demon world has come, with only his trusty assistant, to conquer the modern day human world! It's a little rough from the start, because most people just seem to think he's a cosplayer. Also, due to the worst recession the demon world has had in 500 years, though, he's a little underfunded. For his conquest, he's got to fight the Hero of the human world. She's Ichikawa Kyouko, a distractingly pretty, tough, modern-day girl who happened to pick up the giant sword that marks her as the chosen one. [tethysdust]

A comedy manga about Haman Karn as a modern corporate section chief at an apparel company named Neo Zeon dealing with her insecurities being a 30 year old office lady.