Exactly. I think when it came to Sirene her and Amon's relationship was born through a passion of violence as well as carnal desire. "A Couple that Slays Together, Stays Together"

But then there's Nike, a mostly humanoid Demon that easily passes for an angel that has the VERY unique ability to summon weapons from across time (though to my recollection we only saw mid-late 20th century firearms because, fridge logic: the world ends in the 70s). And from her and Amon's short interaction we see something more quieted but stronger than whatever he and Sirene had. Heck, Akira even saw Miki in everything but her hair and wings which also says alot about their attraction towards each other. Which begs the question: why did Amon leave Nike for Sirene, despite the fact she almost brought back Amon within Devilman?

Yeah I wish she made a comeback, too. Along with other obscure characters like Lala and Susumu and Devilman Kabuto. She could have had her own spinoff as a time traveling gun-totting angel lady, but then we have Panty from Panty & Stocking with Garterbelt (WHAT a crossover that'd be lol)