Two years ago, Mitsuki Kouyama's friend, Eichi Sakurai, moved to America before she could confess her feelings to him. Though she cannot contact him, they made a promise to fulfill their respective dreams: Mitsuki wants to become a professional singer, and Eichi an astronomer. She hopes that one day her music will reach him across the world with a brilliance like that of the full moon. There is just one catch: Mitsuki suffers from throat cancer, which makes her voice quiet and singing strenuous. Her grandmother, who has a hatred of music, insists that Mitsuki undergo surgery to remove the cancer, but she refuses due to the risk of losing her voice. One day, two shinigami—Meroko Yui and Takuto Kira—appear to tell her that she only has one year left to live. This sudden revelation spurs Mitsuki into action, and she decides that with Meroko and Takuto's help, she will become a professional singer in the time she has left. Full Moon wo Sagashite follows the emotional story of Mitsuki and her shinigami friends as they discover what it means to sing—and ultimately, what it means to live.

After overcoming various tumultuous events, mercenary sergeant Sousuke Sagara of Mithril and Whispered school girl Kaname Chidori return to their normal high school lives. Sousuke continues his efforts to assimilate with the civilian population and manage his mission at the same time, while Kaname attempts to support his endeavors (even though his antics often drive her up a wall). However, as their lives calm, new problems begin to appear. The appearance of an independent terrorist organization known as Amalgam and internal conflicts within Mithril threaten to wreak unity into a series of failures and betrayals. And new, powerful Arm Slave models only worsen the situation when the world's peace is at stake. As Kaname and Sousuke face their own inner battles amidst life-threatening fights, will they be able to make the right choices and change their future?

The boisterous student Kaname Chidori and soldier Sousuke Sagara are enjoying a blissful high school life. However, their peaceful days are disrupted by the threatening terrorist organization Amalgam. Leonard Testarossa, a member of the organization who possesses Whispered, seeks to procure Kaname and her knowledge. Kaname and Sousuke's battle against Amalgam starts right in their own neighborhood, which eventually takes them on a hunt around the world. From the exotic lands of Laos to the barren Mexican coast, Sousuke must gather intelligence to bring down Amalgam. Meanwhile, Kaname's abilities grow, but so does her frustration as her resolve withers. Caught up in an intense game of hide and seek, as well as strategic plots, the pair try to connect and push beyond their own limits.

Short specials from the DVDs/BDs.