Through Light and Darkness

(AU were Zeref stayed for the formation of Fairy Tail)
Zeref helps Mavis recover from the shocking loss of her friend of more than half a decade, helping her create the guild now known as Fairytail. Soon though he has an outburst of black magic that Mavis almost sees. Knowing he will lose control soon he makes a quick letter of farewell and disappeared into the night, letting the words on paper explain his sudden absence.

After Mavis healed from the hard death of her friend since childhood, Zera she was building, her newly formed guild. She had multiple feelings of evil magic lingering in the air but dismissed it as the leftovers from the battle at Magnolia. Suddenly she wakes up in the middle of the night with a sick feeling in her stomach. She feels foreboding as she passes room she finds an empty room and a letter of parting. She cried so much she might never see a fairy ever.