From Sherbet Lemon:

An energetic, cheery high school girl named Garam was having a peaceful(?) school life until she runs into a cute boy name Lime. Trouble started as Lime and his best friend, Yuyi moves to her school and monsters start showing up and she's the only one around who can see it. What's more, Lime happens to be a prince from another world who came to this world to find his missing bride who he doesn't even know the face of. As time passes, Lime starts to feel weird around Garam...
...And Garam feels the same except that it wasn't toward Lime but to Yuyi...

It starts as a normal school life story, but it turns to a fantasy from the late middle.

Han Summer (Yeuh-Reum) and Hyun Moo-Heum are very different from one another. While Moo-Heum is a brilliant, yet stunning son of a CEO of one of the most influential and extensive companies in the world, Summer, on the other hand, is a mediocre-looking girl - a plain Jane, who is just under an inescapable debt of 70 million! And to whom? It is none other than Hyun Moo-Heum! In the midst of this dilemma, a mysterious figure enters and intervenes with their lives. Could he be of any help to Summer or is he destined to make her life more complicated than it already is?

From Esthétique:

The cute new heiress of the Jo-Sun throne, Jung Gyuh-Woon! She ends up having two handsome bodyguards by her side! Through all her happiness from being escorted by the knights as the queen, the danger surrounding her slowly creeps closer. Knights, you have to protect the Queen!