According to Sports Hochi:
The Nippon Ham Fighters have been through five double-digit losing streaks in the team’s history:
The Fighters are the third team in NPB history to go on a ten-game losing streak during the year after they finished in first place. The other two teams: 1961 Taiyo (eleven-game losing streak) and 1976 Hiroshima (eleven-game losing streak).
Source: Sports Hochi 4/27/2017