If Shohei Otani makes the World Baseball Classic roster, Hideki Kuriyama might not give him the opening day start. There is enough time in the schedule for Otani to prepare (he would get at least seven days of rest if Samurai Japan makes it to the finals), but there are other factors to consider on top of possible fatigue, like having to readjust to the NPB baseball after working with the WBC baseball.
Extra rest might be beneficial for Otani. Masahiro Tanaka followed a similar path in 2013 (the opening day start went to Takahiro Norimoto) and went on to go 24-0 before heading off to the Majors.
Kohei Arihara and Hirotoshi Takanashi are possible alternate opening day starters, if Kuriyama decides not to go with Otani.