Llama! Llama! Llama! Please give up some crumbs of the Undercover au! You can't just cook so hard, delivered a delicious meal, then disappear leaving us hungry for more! DX
Sometimes, you stay at the office with Eos when he works late. Both of you like the company. You pull up a chair to his desk, and listen to the sounds of him working, watching the evening light fade away... lots of in-jokes, lots of heart-to-hearts, lots of lovely quiet moments together. Those are the times when you'll learn the most about him; his love of classical music, his artistic talents, his cute nerdy appreciation of owls. His dislike of the colour yellow.
He likes when you fall asleep next to him. He can put a jacket over you, listen to your breathing.
You notice that Eos acts quiet and boring when others are around, but while you're alone together, a different side of him is teased out. Something more confident... more playful. You just assume it's because he's shy, and he's opening up to you over time.
You know each other's coffee orders. Sometimes, in the mornings, it's a race to see who can get the other coffee first.
Eos, out of the two of you, is more cynical about the police - you still naively believe in justice, he's much more realistic about the corrupt world you live in. He acts that way mostly because Nightmare's dislike of the force is leaking through... but also because he's trying to slowly plant mistrust in you. He's subtle, feeding you the right information at the right time; showing you which sergeants are having their palms greased, which politicians were let off the hook because they paid off investigators, which sections of the police are under the thumb of organised crime. Sowing the seeds that will make your transition into a life with him easier.
After you caught Nightmare's eye at his party, you start receiving official invitations to his events. Sometimes, you show the invitations to Eos, because you can't believe Nightmare is paying so much attention to you.
The irony is apparent only to him.
Eos 'doesn't like' that you go to Nightmare's events, openly voicing his displeasure at the danger you're in... but you're determined to investigate Nightmare, prove a link between him and the crimes everyone knows he commits, and have him put away.
It absolutely crosses your mind that Eos and Nightmare look similar. But like. You NEVER think they're the same person. Because that's just impossible.
Nightmare is an outrageous flirt. His flirting stays classy, obviously, because he's a classy guy for you. But he makes it very clear what he wants to do to you. You're never prepared for it.
He likes when you argue with him. Calling him corrupt, evil, a murderer. He gets to flirt and play mind games with you... and when the tensions rise between the two of you he can tell you're just as attracted to him as he is to you.
Eos doesn't smoke. Nightmare does.
Nightmare kisses you before Eos. When you told Eos what happened, you lied and said Nightmare is an awful kisser. He's trying to figure out if you're lying to spare Eos' feelings or if he's genuinely lost his touch. Usually, he wouldn't care, but you make him feel weirdly self-conscious.
One time, you (foolishly) got drunk at one of Nightmare's parties. You passed out. When you woke up, bleary and confused with your head in someone's lap, you could've sworn Eos was with you - who else would be looking after you when you're drunk, gently carding their claws through your hair?
... Except it was Nightmare. Letting you rest after you passed out on him.
You refuse to talk about it. You expected him to act smug, or tease you... but he doesn't bring it up again.
He was not prepared for the intensity of your "I need to obliterate this nerd" feelings toward Eos. Despite the amount of flirting Nightmare dishes out, if you get very forward with Eos he will be caught off-guard and get extremely flustered.