Izuku was only two months old when he was taken by an unsealed Kaguya Otsutsuki. She became his mother and Izuku became a member of the Otsutsuki Clan. He was a prodigy with chakra and with its manipulation. Kaguya wanted to protect Izuku for the rest of her Clan so she few him chakra pills made from her own chakra. She died as a result. When she died, she sent Izuku back to his old world to prepare for the arrival of the Otsutsuki Clan and to prevent his fate of becoming a sacrifice for an even more powerful God Tree.