Crimson Legend

Orphaned at a young age, Ayaka grew up as a very strong and willful, but beautiful girl under Gai's care. She hides a secret that whenever she becomes strongly emotional, a crimson pattern of a phoenix appears on her back. On her way home one day, a strange guy named Kira tries to kidnap her, but another strange guy named En appears to prevent it. Thus begins the Crimson Legend, a tale involving the mysterious powers of the phoenix and the enemies of those who possess it.

Also included in volume 4 of this series is a one-shot by Asagiri Yuu titled "Senryoku no Memory" involving a guy and girl in high school who are coping with the death of a loved one.