Long ago, Miura and Mori spoke at length regarding where he wanted to go with the story and what the ending would be.  Miura also left notes and memos going in-depth about his plans.  According to Mori, Miura's assistants reached out to him regarding the continuation of the manga.  As Mori is one of the only people to know what the ending will be, he is the best bet to complete the story as Miura would want it.  And, as one of Miura's friends going all the way from high school, he is the perfect one to take up the challenge.  Mori has said that he won't be adding his own spin on things and will only proceed with the story as he remembers Miura telling him.  

 

Berserk was left with its current arc, the Fantasia arc, incomplete.  Mori's plan is to complete the arc, and then begin and finish one ultimate arc which has yet to be revealed.  The next chapter of Berserk will be released on June 24 in magazine Young Animal.  Mori will be formally credited as supervisor, and Studio Gaga, which consists of Miura's assistants and apprentices, will create the actual artwork.  

 

If you're unfamiliar with Kouji Mori, he is a veteran mangaka in his own right and is best known for the manga Holyland, as well as Jisatsutou (Suicide Island) and its prequel, Muhoutou.  Both he and Miura are published in Young Animal magazine.