What is the fine-grained topic of the following text: Hiroto Saikawa, tipped to replace disgraced Carlos Ghosn as Nissan chairman, was long considered one of "Ghosn's children", a loyalist to the powerful tycoon who owed him everything -- but then oversaw his downfall. Only return the topic.
Hiroto Saikawa's succession of Carlos Ghosn as Nissan chairman