In episode 117 - Thunder Roar at about 7:50 into the episode Zeref regains consciousness and attacks with a technique resulting in the following picture.
MANGA SPOILERS BELOW
Orphaned after Dragons killed his parents and his little brother, Natsu, an extremely young Zeref became a student at the Mildian Magic Academy, where he researched the connections between life, death and Magic to revive his brother. After creating things such as the R-System and the Eclipse Gate, he was expelled from the academy for breaching the sacred teachings of Ankhseram, however he was cursed by Ankhseram and then killed everyone around him with his newfound, unwanted Curse of Contradiction.
Thus simply speaking Zeref wants to die, but can't and the Ankhseram's Curse of Contradiction kills everyone around him instead
Source: Manga. Wiki page: Only Open for spoilers on Zeref, Mavis, DragonSlayers and the Heartfilias