Childhood friends Tomo Aizawa and Junichirou "Jun" Kubota do everything together, whether it be training or just enjoying a fun day out. Anyone would think that these two are best friends for life. The only issue is that the tomboyish Tomo is in love with Jun, but he regards her like a brother. At the start of their first year of high school, Tomo confesses her feelings to Jun. However, her rough mannerisms and lack of hesitance to throw a punch do nothing to sway Jun's heart. Realizing that he will remain indifferent to her affections unless she does something about it, Tomo must find a way to knock some sense into Jun and open his eyes to what is right in front of him.

Bundled with the 11th volume of Kanojo ga Flag wo Oraretara light novel.

Unaired episode included with the Blu-ray box set.

The story begins when high school student Kazuki Muto is killed one night saving a mysterious girl from a monster, only to wake up in his school dorm, believing it to have been a dream; however, he soon finds out that dream wasn't a dream at all when a giant serpentine monster attacks him and his sister. Tokiko Tsumura, the girl he saved, explains that the monster is a homunculus. Kazuki had been attacked and killed by it when he was rescuing her; however, she, feeling responsible for him, revived him by placing a Kakugane medallion in his chest, serving as a replacement heart. The Kakugane, as Tokiko explains, is an alchemical device that, when activated, takes a certain form based on the Kakugane's user, forming a unique Buso Renkin. The Buso Renkin is the only thing that can destroy a homunculus monster. Using this, Kazuki creates his own Buso Renkin (the "Sunlight Heart," a huge lance). Along with Tokiko and her own Buso Renkin (the "Valkyrie Skirt," an execution scythe), Kazuki joins the fight against the homunculi and their master.