Basically, you have this girl name Amu who is misjudged by her peers because she dresses 'punk'. So one night she wishes to be the 'real' her, which is a girl that loves to transform into a pink Sailor Moon. She wakes up to find three eggs in her bed, or what they call themselves as 'charas'. (In Japanese, Shugo Chara means my Guardian Characters-NOT THE SAME AS MY GUARDIAN ANGELS)
In the chara world, there is a coorperation called Easter (Yes.) that want to go after the Embryo (YES.), which is an egg that will grant the wish of whoever captures it. Easter has some pretty crappy tactics as to getting the egg and they end up using a girl named Utau Hoshina (Later revealed to be Utau Tsukiyomi) for her singing talents (In Japanese Utau means 'sing') to literally 'sing' the X eggs out of an audiences' chest.
Ikuto Tsukiyomi, possibly one of the hottest shoujo boys you will ever meet, is blackmailed and signed to Easter by a contract his father, Aruto, made the day he decided to marry Utau and Ikuto's mother, Souko. He must work for Easter until they find the Embryo. Aruto was a famous violinist, and Ikuto posesses the same talent.
It's a pretty good psychological story if you look past the kiddie factor.
Do not, under any circumstance, watch the anime. You will be very disappointed.