Tropes

Ambiguous Gender: We never see the second Butterfly Amazon's human form, making it impossible to tell.
Made of Iron: The second Butterfly Amazon is incredibly durable, consistently tanking damage up to and including being impaled.
Razor Wind: The Butterfly Amazon's molted form is capable of hurling it's wing scales to emulate this.
Slashed Throat: Amazon Omega's Violent Punish kills the Butterfly Amazon in this way.
Slasher Smile: A rare heroic Kamen Rider example when Haruka displays one.

Recap / Kamen Rider Amazons Ep 6 For What I Fight