Update: Genji's Oni skin is available once again through the "Nexus Challenge 2.0." You'll only have to play five games in Heroes of the Storm — in Versus A.I., Quick Match, Unranked, or Ranked modes — to unlock the Oni skin in Overwatch. You can earn the Oni skin until May 1. The original story — from when the Oni skin was available at the end of 2016 — follows.
At BlizzCon, Blizzard Entertainment announced that between Tuesday and Jan. 4, Overwatch players can earn an exclusive skin for Genji called "Oni" by putting some time into Blizzard's free MOBA, Heroes of the Storm. In addition to the skin, players will also unlock an Oni player portrait and spray.
The thing is, not everybody who plays Overwatch likes MOBAs. If you're downloading Heroes of the Storm with one thing and only one thing in mind — that awesome Oni skin — here's how to earn it as quickly as possible so you can get back to Overwatch ASAP.
'Overwatch' Genji Oni skin: The fastest method to unlock the skin, spray and portrait
The basic requirement to unlock the Oni skin is to complete 15 games of Heroes of the Storm "with a friend" before Jan. 4. If your usual friends aren't available, the Overwatch Reddit can match you with another player who's trying to get the Oni skin, too.
The best mode to load up for this is co-op vs. AI, with your opponents set to Beginner — the absolutely lowest difficulty level there is. Typically, a match of Heroes of the Storm can take upwards of 20 or 30 minutes, but if you have a healthy team makeup, you should be able to plow through a match on the beginner difficulty in 10 minutes or less. If you're counting, that means it should only take you about two hours total to unlock the Oni skin.
If that's too much time to commit to a game in a single sitting that you didn't want to play in the first place, you can always stretch it out of the course of several days. You have until Jan. 4 to finish all 15.
If you're playing on console, the process for linking your Battle.net account to your console is easy — the steps are outlined here.