Shugo Chara! Vol 4

From the Kodansha edition

CHARACTER SWAP! Amu has three Guardian Characters, reflections of her true self. But now a fourth egg has shown up at the start of a new school year. Everything has gone wrong, and Amu has no idea who she truly wants to be. Meanwhile, her rival Utau has rejected one of her own Guardian Characters. Is it time for the two to trade Guardians? Is that even possible? This volume of Shugo Chara! includes special extras after the story!

Source: Anime News Network Encyclopedia