“When the owner of the four-leaf grimoire is filled with despair, the five-leaf clover grimoire will be born.” Patry is filled with despair after learning he had been manipulated by the devil all this time and turns into a dark elf. He then starts attacking Yuno and Asta, fueled by nothing but hatred and malice. Somehow, becoming a dark elf had made Patry even stronger, which gives Yuno and Asta an even harder time fighting him. Then Captain Nozel appears before them. Nozel happens to have the best magical attribute to fight against light magic, mercury magic.
so that they can cover each other's 
weaknesses when they go on missions.
.كي يغطوا على نقاط ضعف بعضهم في المهمات
per aiutarsi a vicenda, compensando ciascuno 
le debolezze degli altri durante le missioni.
para que suas forças possam cobrir as
fraquezas dos companheiros nas missões.