Kusuriyubi Hime

From Shoujo Crusade:
The qualification for a princess is for a prince to be beside her. Hinaki, who wishes to become a real princess, is a genuine girl. Around Hinaki there is Yume-senpai, who is almost annoying but is really just trying too hard, and other boy followers, but no one is Hinaki’s “prince”. The “prince” who should be beside Hinaki is inside her ring…!?
From Baka-Updates:
Houjou Hinaki is a young girl who has in her possesion a ring, a gift from her father. Anyway, this ring is not an usual one. When she kisses it, a young noble man named Sae appears in front of her and grants all her wishes. However, Sae is trapped in the ring and can’t tolerate much time outside and together with Hinaki and her freaky schoolmate Yume-senpai, tries to find out a way of how he can escape from the ring’s prison.