Sephiroth smiles himself - it's almost sly. He recognizes that interest, and respects it. Whether or not this man could actually be any challenge for him, the drive to attempt it - and likely to potentially better himself in the process - is admirable. And Sephiroth's not without interest in sparring himself - even if the odds are wildly stacked in his favor. It's easy for him to rely on his overwhelming advantages to win engagements, without taxing his skills. But when faced with opponents forced to rely entirely on skill or tricks to even attempt to challenge him...that helps him learn new things himself.

"In my world, SOLDIERs like myself are enhanced through...questionable procedures," he replies. "But three of us, in particular, were altered to such an extreme that there was no one outside of us who could hold their own against us in our prime. Biological superweapons...and we're accustomed to being deployed as such. I don't mean it as any disparagement of your skill when I say that, without enhancements, you'll likely find me an impossible opponent. Humans aren't equipped to face me single-handedly."

In a way...it's the talk about sparring that decides him. The interest had already been simmering, simply from the other man's attractiveness and his own desire - and the lack of compunctions he's currently feeling about indulging his desires, which he's only been holding back with difficulty because speaking to someone who gives him such powerful memories of the military helps call back his own discipline. But adding in the prospect - the pleasure - of sparring, of facing an intriguing new opponent, and it's more than enough to fan the spark of his interest into something hotter.

So, with his invitation clear, Sephiroth relaxes that discipline of his. He leans down, a gloved hand brushing Zechs' hair a bit more out of the way as he kisses him. It's heated, but almost slow at first, as if giving Zechs time to come up to speed and match him.