Shun Takayama blasted the first home run of his NPB career during a Yakult game on March 31. The home run led off the start of the game and came against Kyle Davies. Takayama is the first rookie in franchise history since Tomochika Tsuboi in 1998 to hit a lead-off home run for his first career blast.
Source: Tokyo Sports 3/31/2016
[UPDATE 4/1 @ 6:54am]
Thirty Japanese players, including Takayama, recorded lead-off home runs for their first career home runs (eleven Central League, fourteen Pacific League, five single league). The last player before Takayama was Shogo Nakamura in 2015. Of the thirty, ten were rookies, including Takayama and Nakamura (seven since the two league format began in 1950).
Since the start of the two leagues, three players have recorded lead-off home runs in the top of the first inning for their first career home runs: Yuki Miyazaki in his second year in 2012, Seiya Suzuki in his second year in 2014, and Takayama in his first year in 2016.
Takayama joined Yoshito Fujino (July 1, 1944) as the only rookies in NPB history that can say their first career home run was off the first pitch of a game.