Birkin followed Stein's gaze for a second and raised an eyebrow after seeing nothing there. "I think she'd really appreciate it if you were more officially her partner rather than secretly trying to kill her and all that." He blinked a few times. That would probably get needlessly complicated over time, wouldn't it? "What's holding you back from dropping that mask and joining up with her then?" He tilted his head in curiosity. To an extent, Birkin genuinely wanted to know what Stein did to redeem himself so to speak in everyone's eyes. Maybe he could use that to his advantage and get everyone on his world to trust him so he could launch a sneak attack.

"I like your house by the way. You certainly put a lot of yourself into this building." Birkin couldn't help but smirk at Stein. He had an... Interesting sense of interior decorating, to say the least.