Couple of the century, Crystalized headcanons!
Harumi did die, The Overlord had found her body soon after and used the crystals to resuscitate her
The crystals were adept at mimicking a regularly working body so Harumi barely noticed until she was given more power and felt the crystals inside her body spike and grow (she grows crystal devil horns cause I said so).
Miniscule crystals flow through her blood stream, discoloring skin and such
I plead mania as her cause (RIP Harumi's writing she did NOT deserve that loll) her consciousness was brought back in The Overlord's plane as well as revived with a destructive crystal, her revival was a form of reimagining Harumi through an evil lense, making her manic in a way, the crystals manipulate the way she thinks and feels.
Clinging to her safety net Harumi rebuilt Mr.E, being the only one she has ever trusted but because she did not actually have his previous parts including what made him who he is she rebuilt him based on her own memories and feelings using the crystals
She herself is distorted as well as her memories so the newly built Mr.F truly is the new model, so close yet so far from the E she remembers
Although it pains her to see an imitation of him, Harumi knows it's better to have a piece of him with her then none at all.
Mr.F uses a piece of the crystal in his chest as a new power source, continuously growing inside of his mechanical body. Seeping through his faceplates, or any opening it can
The crystals growing from within him pulse, making his visible crystals look almost alive from the inside
He uses the energy from the crystal to act as fuel, this is why he has many different tubes attached to him.
The most notable difference in Mr.F and Mr.E is his use of guns, this was not his fighting style at all considering he was close combat (most likely because Zane was ranged) I like to think this difference pains Harumi in a way because it is so different
