Amanoiwato Hime

The time is probably the 21st Century. In the Hinomoto Kingdom where the king has the kingdom under control with somewhat of peace, 3 rookie military officers, Haru, Natsuki, and Touma, are assigned with a very special mission: To protect the King's daughter! The three rejoice at this unexpected mission that their lieutenant provided them with, and they quickly arrive at the princess' room but find out that the princess is different than what they had expected..... A princess guardian comedy now begins!

(Source: Mangaupdates)