The newest reports reveal that Yusei Kikuchi was indeed the target of Hiromoto Okubo's abuse. While Kikuchi was not named in the report that the Lions made public earlier today, someone with the club (perhaps a leak) made it known to the press.
It also seems that earlier reports of Okubo getting upset that a player snitched on his methods of punishing for tardiness were true: someone reported to the Lions' player's association that Okubo was handing out big fines to to tardy players. The player's union then approached Okubo and ask him to stop. Okubo assumed that it was Kikuchi that reported him and apparently became violent with him. Exactly what he did was not released to the public.