Succombing to Kazuya's devilish charms (before his intimely death), Jun is inextricably drawn to Kazuya. . . and Jin is the result. When Kazuya's body burns in a volcano, the devil possessing him seeks a new host and picks the unborn Jin. . . like father like son.
Jun has other ideas though, and manages to prevent the devil from entering Jin's body. Having defeated the devil, she whisks Jin off to the desolate Yakishima to raise her son alone.