Hi! I'm glad I made you curious. That's really what I aimed for. Sorry.

So back to your question, it was Ambrosia. Ambrosia made Athan an undying. Ambrosia literally means "immortality" in Greek. In addition, the food of the gods are nectar and ambrosia. These made the gods live forever.

She reached to his face touching only his chin leaving a stain of her blood.

When Rosia left that blood in Athan's face, he became an undying. The people chasing them were actually after Ambrosia, after immortality but Athan knew nothing about it. Since she died that night, the people after her stopped chasing her husband and daughter after they shot arrows at them that's why Athan and Amara never faced danger even after staying at that village for a long time.

They moved from town to town carefully for their security...

They thought they would still be chased but, no. Not anymore. But maybe when they found out about Athan, that could change. We'll never know.