After the Tournament of Power ended nearly 4500 years the ago the Z-fighters all lived peacefully lives fighting, laughing, and eating in otherworld until the The Kais gave them the opportunity to live again in another universe but at the cost of memory loss. Everyone took the chance to get reincarnated again and live to see another earth all except Goku who wanted to stay behind and fight strong opponents when they died and came to otherworld. Truthfully though he didn't want to forget his family and friends. Through some very, very convincing persuading he reluctantly was born again into the world of angels, fallen angels and devils.