Priest manga volume 4: Harbinger's Song

Before Ivan Isaacs became the undead pilgrim who battles Temozarela's forces, he was just a mortal man with the usual human failings. Orphaned at an early age, Ivan was adopted by Jacob Isaacs, a wealthy frontiersman who wanted his only daughter, Jenna, to have a companion. In the solitude of the Isaacs' homestead, the two siblings developed stronger feelings than their father or society would allow. To escape from his desire, Ivan entered seminary, where he found a new interest: the study of ancient religions. Nine years later, Father Ivan Isaacs is still haunted by memories of his true love. But a new figure has begun appearing in his dreams—a Knight Templar, a holy defender of the crusades. Now Ivan stands at a crossroads. One path leads to ancient demons, the other to a forbidden love.