Is this the first time VTB is in charge of anime op?
Not quite. Kizuna Ai herself sang the OP for the vtuber anime Virtual-san Looking. I believe it is the first time that a Hololive member has sung the OP for an anime series, although Suisei sang the theme song for the trapezium anime film, Aqua, Subaru, and Nene sang the ED for The Great Jahy Will Not Be Defeated!, and Calliope sang the ED for the Suicide Squad anime.