What Im guessing happened was Jahad killed V and Arlene's kid (Baam), and as a revenge plot, she somehow asked somebody outside the Tower to keep V's soul in said dead kid's body until it healed enough to take it over.
But some kinda way the dead kid woke up first. Prolly because of Rachel talking to the corpse every day.
I also think Rachel is only an Irregular in the sense that she was outside the tower. She had to be born IN the tower. She had no shinshu control until she passed some floor tests.
Her and Wangham are prolly Arlene's kids by Jahard from before she met V.
Meanwhile, Baam technically an Irregular because he wasn't born outside the tower, but his soul came into existence outside the tower.
It would make sense why Baam is "empty" on the inside. He was supposed to hold V's soul/power, who would be an "Irregular" twice over.
Definitely an interesting theory. Here's a chapter with some key points to support some of the ideas:
What do you desire? Money and wealth? Honor and pride? Authority and power? Revenge? Or something that transcends them all? Whatever you desire—it's here.
www.webtoons.com
I know the story claims V committed suicide, but the message and decision to take himself out feels sketchy to me. I could definitely picture Arlene escaping the tower and having her portion of the key and whatever was left of V stored in the vessel (aka Baam). I think the Key bit might explain why Baam can just break spells and curses like it's nothing (making its power literally to unlock those spells/curses).
Semi-related, Luslec and Arlene both have Grace in their names and specialize in spells. So I think it's a good bet they're related, maybe siblings. I remember having a theory about Luslec's eyes, but I have to revisit his references and appearances to recall what it was...
I think Phantaminum was the God she met outside the tower. Since he's an axis, he can dictate a story into a reality, which is where I think the prophecy about Baam comes from.
I differ with you on Wangnan theory. I think Zahard tried to make copies of himself through the Workshop and considered it a failure. It seems like the Captain character looks like them too, and it'd be funny if Karaka does beneath the armor.