Nanatsu no Taizai OVA

After 700 hundred years of guarding the fairy forest, the holy saint sworn to protect the Fountain of Youth gets a persistent visitor that doesn't seem to act much like any of the other humans or theives that have come before him. As an OVA of the running series "7 Deadly Sins" on Netflix, Bon's backstory is extended to show how his relationship grew with the holy saint of the Fairy Forest Elain.