All Shinta wants is to find a girlfriend, and constantly falls in 'love at first sight' with his classmates. Unfortunately for the boy, none seem to reciprocate his intense feelings, and thus, he does the only thing he can think of – he visits a local shrine to hopefully have his wish granted. Much to his surprise, Shinta encounters a god at the shrine who decides to grant his wish, and the next morning, Shinta wakes up next to the lovely goddess Isana. But all wishes come at a price – it's that time of year when gods throughout the world battle it out for territory, and each deity like Isana must use a human as their champion. Now, Shinta must fight countless enemies for his newfound girlfriend, even though she doesn't seem to want to give him the time of day!
Both manga feature a rather cute married couple as main characters, so if you liked one series for that, you'll probably won't be disappointed with the other one. This said Samurai Usagi seems to be a tad more serious than GAN☆KON.