"Who exactly is that woman? Why don't I feel strange when I see the aura of that woman?"
Leon thought when he saw Emily for the first time. Maybe he didn't know that Emily had a special past relationship with Nicholas.
Because of that, he may feel Emily's presence, which is familiar to him.
In the past, when Nicholas was young and had not met London, he had such a beautiful romance with Emily.
In the past, Nicholas had felt that Emily was his soul mate. But all that changed when he met London; he immediately found a true soul mate because he met with London.
When Emily discovered that Nicholas had tied a relationship with London, it could be said that Nicholas and London had imprinted each other.
She decided to leave her old life; she joined the Peace Organization to relieve her pain due to the betrayal of her previous love.