I mean, not to rub salt on the wound, but...yes, it's Kagari's fault.
I mean, if AT LEAST there was SOME inner conflict, like that Sekirei being a friend, or Kagari never having terminated a Sekirei, or SOMETHING... You could argue that he was trying to inflict minimal damage, or this or that. But nope.
He just turned his back on an unfinished enemy cause reasons.