Spoilers ahead!!
It was revealed that he did that to save her from the temple (temple and that spirit are evil here, and that Holy spirit kidnapped MC's mother and made her preggy) MC's mother asked him to save mc (mc can't live past 30 in any of her lifetime no matter what)(I didn't understood much but MC's mother kind of had dual personality type thing, AND THAT WAS MC HERSELF WHO ASKED TO SAVE HERSELF and sometimes her mother returned and was confused and scared that's why she killed his brother because she was confined somewhere strange) (yeah mc kinda time traveled)
That spirit wants to merge dimensions (Idk the reason but it's something bad) and whenever mc use alchemy the cracks between dimensions widen and more monsters run wild
And it's actually reverse harem, mc kinda forgive everyone, and she felt something for her "not father anymore", the backstory of him was genuinely sad so okay I guess.... And she fks her husband, her two "not brother anymores" and there will be one more male lead whom everyone liked the most, BUT HE IS SOMEHOW RELATED TO HER (he is ex-priest and in that temple everyone is related, they do ince*t to keep themselves pure to maintain holy powers, so mc is the daughter of holy spirit/Holy father/pope) but this ex priest mc kin better than other MLs tbh
There were many dimensions introduced AND IT WAS SO CONFUSING FOR ME TO READ THE SPOILERS I'M STILL CONFUSED, somewhere she was adoptive sister of his ex husband, sometimes she was living fine with her brothers and many more Idk
I couldn't bring myself to finish the novel because mc was great in first half but in second half she lost her "smart-ass iron wall lady" character, she became a bit dumb and gullible. I hated that and dropped it, and read tons of spoilers
https://novellatte.blogspot.com/2023/07/spmb-chapter-1.html?m=1 It’s up to chapter 118 if I’m not wrong

For those who didn't like reading the spoiler please skip this
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Just a bit of spoiler from the novel that I only read half .
The father can't die and can't get old because of her mother alchemy that's why the Duke hate her mother and mc biology father because mc mother killed his brother and put a curse on him , mc real mother is the Korean mother that staying with her for 12 years and she's the real genius alchemist.
Very complicated story but the point is , mc real father is the divine spirit from the great temple and her mother Junhwa korean mother , and Duke father kinda of kidnap her from the divine spirit (mc father) and make her her daughter , I don't know the real reason why he do that , I thought because he want a revenge but apparently not,
About mc alchemy , why mc father forbidden that because alchemy is the source of the dark power , a power that comes from other dimension, that's why he forbidden mc to continue .
I only can read up to ch 152 and there's still more than 150+ chapters ahead, and I can't take it to read anymore.