[Fullmetal Alchemist: Brotherhood] Whatever You Can Imagine

Starting a new story on my birthday~ Once upon a time, there was a protagonist who transmigrated. When he transmigrated, the person who sent him off promised that he'd end up in Fullmetal Alchemist: Brotherhood. But when he arrived, he couldn't see a thing. The only thing he knew was that he'd become a baby. By the time he could finally see... Edward, with his whole body intact! Roy, with a beard! And a little chubby baby about his age beside him! Once he learned the language, he discovered... The male lead was born in 1905, but I wasn't born until 1925! Who the hell ate those twenty years in between?! Still, this kind of farming life [Are you sure?] is pretty wonderful. He gets to grow up with a whole bunch of brothers and sisters, researching human transmutation and tinkering with mass-energy conversion every day... After thirteen years of living in a dream, he finally learns that the real drama is just getting started. Here is the kindest Truth: "Wait, does that thing even have a conscience?!" Here is the most oblivious male supporting character: "As the author, it's terribly irresponsible to simply label me a 'male supporting character.' What if people get the wrong idea?" Here are the most troublesome male and female leads: "First, I'm really not sure I count as a 'woman.' Second, are you even sure which one of us is the male lead?" And there's also the most powerful cheat. Readers uncomfortable with a man becoming a woman, please be warned. This is only a past-life setup, and the protagonist adapts to her female identity quite well. Childbirth is involved, but the process won't be described. Theme: