That is Chaos;Gate’s choice… ~That is, the Gigalomaniacs’ version of Steins;Gate’s choice~
This short story was included in Nitro+ Complete a few years ago, set in 2009 Shibuya, it details a chance encounter between Okabe Rintarou and a rather stoic ChäoS;HEAd heroine, Aoi Sena.
I would suggest having gone through both ChäoS;HEAd (ideally the VN) and Steins;Gate before you read this, or else most of the events in the story will be lost on you.
I was asked to translate this a while ago and I finally got around to it, so here you go.
I hope you like it