Himesama Gentei!

This is the first title by Princess Sugar. Celina is the princess of the prosperous western European country of Mellberg and came to Japan to study at a normal school while concealing her true identity. Since she is a distant relative to Yuu, she ends up living in his house. One day, the princess of the resource-rich country of Marualand, Olivia, was exiled to Japan in a coup d’état. Quickly gaining notice around the town, she was treated like a honored guest. However, Yuu disapproved of her snobby attitude since he had grown accustomed to being around princess Celina. Then, Celina told Olivia not to be near him as he is her most precious person. Not backing down from the challenge, she states that she will make him hers.

(Source: VNDB)