To rear - in that intransitive sense, 'to become a more menacing presence' - is not a very common word; it seems to me to be dying out, except in the idiomatic phrase 'rears its ugly head': When two people start sharing a house, it's never long before the problem of cleaning the bath rears its ugly head. In the case of a person, the word 'loom' is more common in my experience - Suddenly the headmaster loomed over his shoulder; and with the preposition 'over' I'd also expect the word 'tower' - His sister towered over him.
... but "towering over" doesn't have the connotation of extreme closeness; when you loom over someone you're invading their personal space, but when you tower over them you're just much taller. You can 'loom' even if you're quite small, but towering requires height!
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