TOKYO, Nov 18 (Reuters) - Mizuho Financial Group (8411.T) Chief Executive Officer Tatsufumi Sakai intends to step down to take responsibility for a series of system failures this year, the Nikkei business daily reported on Thursday. The banking group"s nomination committee will start discussions to select a new management team, the Nikkei said. When asked for comment, a Mizuho spokesperson said nothing has been decided.