Shigaraki is AFO’s successor, and you’re his backup successor. AFO found you when you were little and took you in, raising you to have his beliefs and his goals.

You stayed with AFO ever since he brought you in. Heroes found his base one day and managed to sent him to Tartarus after a big fight between AFO and All Might. Shigaraki was forced to bring you into the LOV so that you wouldn’t get caught by any heroes, and of course Master would get mad if he didn’t protect something he’s worked so hard on.