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's point, declares him her boyfriend . It's obvious she's not... quite... right... A hilarious, slightly ecchi love-comedy ensues.

From Dynasty Scans:

10 years ago, high-school student Sanpeita dreamed he was engaged to a beautiful girl. One morning, an unknown homely girl suddenly pressed him for marriage. The homely girl was named Kemeko.
In order to escape, Sanpeita left for school where Kemeko followed and showed up with an uproar. A larger disturbance was when Sanpeita was targeted by a rice cooker on the school's rooftop.
As Sanpeita and his childhood friend Izumi were being attacked by the rice cooker, Kemeko saved them both. What is the girl's true shape!?

Tribute anthology for Azumanga's 10th anniversary, by various artists.

In a land far, far away exists a tiny kingdom named Momonofu. It is ruled by the Momonofu family – that is, the king, the queen, and the prince. Well, the prince is actually a girl, but that is just a trivial detail. The prince’s princess’ hobbies are eating snacks, collecting stuffed animals and dreaming of world domination. Enter Miyamoto, the faithful butler of princess Apricot, who’s actually a super sadist and possesses superhuman butler powers. Together with various other companions they set out to conquer the world – or at least to mess up princess Apricot’s daily life!

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.