Well, technically 99 years, so not quite a century. The last guy to do it was Babe Ruth in 1919.
And it’s even more difficult for Shohei because he doesn’t bat when he pitches. (He never started any inter-league games.) On the other hand: (1) he came nowhere near the Babe, who pitched 133 innings and smacked 29 homers; (2) Ruth only hit three of those homers in games he pitched.
No player has ever hit more than 9 homers in a season in games he pitched.
Too bad about the injury. Through May 20 he was 4-1 as a pitcher, and was hitting .321 with a .986 OPS. He may still win rookie of the year, despite missing a month as a hitter, and three months of pitching. He never pitched in August, but he batted .328 with an OPS over 1.000 as a full-time DH. I’d say the kid can play!