Lost to history and buried under the ashes of its ruin, the ancient city of Pompeii was once home to many great warriors. High school student Keidai Saeki is the reincarnation of Sirix, one of these warriors, and he retains the memories of his past life.

While at school, Keidai does not openly share the truth of his memories. The only one aware of them is his best friend, Mii Serizawa. In her past life, before the destruction of Pompeii, Serizawa was Loleus, Sirix's male best friend. However, unlike Loleus who felt nothing more than brotherly affection for Sirix, Serizawa is in love with Keidai.

Unaware of Serizawa's feelings for him, Keidai yearns for Serena, his wife from his past life. But his hopes of their romantic reunion are dashed by the arrival of his new neighbor, Yuuma Ujoh. Though he does not remember, Yuuma is the reincarnation of Serena, and he has fallen for Serizawa! Plagued by Sirix's memories and regrets, Keidai must choose to remain in the past or pursue a new future.