Genji thrives on movement and assassination. He has the potential to deal out massive damage, but he does have some counters in the game. Heroes that negate or match his movement are critical, and beam weapons cannot be deflected with Genji's ability. While this list is non-exhaustive, it should get you started. I'll be splitting them out by role, and these observations are based on my experience in game and in watching professional matches in the Overwatch League.

Support:

• Lucio

Lucio also thrives on movement, using wall riding and speed boosts to effectively move around maps. His boop (right click) is also a great tool in keeping Genji away from not only you, but from your teammates. If you see a Genji homing in on a teammate, use your superior movement to boop him away. Peel for your team, as it's called! The boop will also do damage through Genji's deflect, which is good!

• Brigitte

Arguably the best support to counter Genji. Their effective ranges are about the same, especially when a Genji is attempting to assassinate someone. Brig can stun heroes with her Shield Bash, a short range move that is great for quick characters like Genji. Her Whipshot move can also knock Genji away from you or your teammates, while providing a constant heal for your in-range teammates if you make contact.

• Moira

Moira's kit is also a great counter to Genji. Her primary attack is a lock on beam that cannot be deflected. She also has her Fade movement option, which renders her invisible/invulnerable for a short time, allowing her to evade an incoming Genji, repositioning to a more superior spot while Genji's cooldowns are active.

An argument can be made for Mercy, however her kit is about movement and avoidance, so she can be useful in simply getting away from Genji, provided your teammates don't leave you hanging. The other supports (Ana, Zenyatta, Baptiste) don't have a lot of movement options, so they are susceptible to Genji's kit. Baptiste can save a teammate with his Immortality Field, but it's far more useful in saving groups of teammates, rather than one solitary team member.

Tank:

• Winston

Winston is, in my opinion, the best counter to Genji. His movement cooldown is very similar to Genji's dash cooldown, so he can follow Genji with ease. His primary attack also deals damage through Genji's deflect, and typically has enough range to hit Genji's double jump. His deployable bubble shield only helps in these engagements, but the shield should probably be prioritized for other engagements.

• Zarya

Zarya is another crucial counter to Genji. While she does not have movement abilities, her self shield and team shield are invaluable. If you see a teammate getting attacked by Genji, providing them a team shield bubble will save their life, and probably leave the Genji a little helpless, as his cooldowns will have been used up attempting to assassinate that teammate. Her primary fire is also a beam weapon, which cannot be deflected by Genji. Just be careful, as Genji can deflect Zarya's Graviton Surge ultimate.

• D.VA

D.VA is another solid counter, and although her damage output may not be too viable against Genji, she does have the tools to chase him down, put him out of position, and protect her teammates with her Defense Matrix, an ability that absorbs projectile and hitscan weapons.

The case could be made for Reinhardt or Roadhog, however Reinhardt should not be the one primarily dealing with a Genji unless he is in range of his hammer swings, as Genji can deflect Firestrike, and Reinhardt's charge is not likely to work against Genji due to his superior movement abilities. Roadhog can get lucky and hook a Genji in close to him, however Genji can deflect the hook OR buffer a reflect for after the hook ends, allowing him to instantly deflect any of Roadhog's followup shots. Orisa, Sigma, and Wrecking Ball are not great counters to him, though a better player than I at Wrecking Ball could make a good attempt at countering due to his crazy movement, and the natural way his movement deals damage/knockback.

Damage:

There are a handful of characters that can handle a Genji.

• Genji

The man himself. What better counter to your kit than your own kit?

• Doomfist

The bulk of Doomfist's attacks are physical, non-projectile and non-hitscan attacks. I believe Genji can deflect the damage from those physical attacks, stopping them from damaging him, however Doomfist's attacks usually deal knockback and stuns, knocking Genji out of his abilities. Doomfist's movement options can easily keep up with Genji.

• Echo

The most recently added hero as of writing this post, Echo's kit as a flying character allows her to freely move around maps, and although her primary and secondary fire are projectiles, her Focusing Beam attack is a beam that cannot be reflected, and deals increased damage to targets with less than half health.

• McCree

Although his primary and secondary fire are hitscan shots, McCree does have a movement option that also reloads his gun. His Flashbang stun can be used to great effect against Genji, however he can deflect the stun, turning the advantage against McCree. Sending the flashbang at Genji's feet is a semi-effective strategy to avoid the deflect.

• Mei

Mei is an excellent counter to Genji. Her primary fire counts as a Beam weapon, while also slowing and eventually freezing her target. This is very effective against Genji's movement, slowing him down and mitigating his crucial movement options, like his double jump. Mei can also provide ice walls to save a teammate (but be careful with this, as it's easy to mess up and do more harm than good), and her Ice Block ability is a great self-preservation tool, restoring Mei's health and allowing her to strategize for a few seconds.

• Pharah

Another flying character with projectile attacks. While these can be deflected, they deal splash damage if they land nearby, and deal crazy high damage if the missiles hit directly. Not the most effective Damage counter, but useful.

• Sombra

Sombra's kit is complicated, and she is a difficult character to learn and master, but she can render Genji utterly useless with her Hack ability. When hacked, Genji cannot double jump, wall climb, dash, or deflect. Working with your team and calling out when a Genji (or any enemy) is hacked can be a great way to deal with him.

• Symmetra

Symmetra's range is limited, but her primary attack is a beam that cannot be deflected. Its damage also increases the longer it is connected to an enemy or an enemy shield. Additionally, Symmetra's Sentry Turrets are also beam weapons that slow enemies, which can be very effective against Genji. They only have a very small amount of health though, and are easily destroyed.

• Torbjorn

The case can be made for Torbjorn. While he doesn't have a lot of movement options, his turret can lock onto Genji, tracking his movement if he is within Line-of-Site of the turret. While it may be more of nuisance than anything else, it may force the Genji to play more safe, or lock down certain flank routes that he may take.

• Tracer

A good overall character, her focus on movement can help her deal with a Genji. Her guns are hitscan though, so Genji can still deflect.

The remaining Damage characters Ashe, Bastion, Hanzo, Junkrat, Reaper, Soldier 76, and Widowmaker do have some potential against Genji, but the odds are stacked against them based on their various kits.

The overall idea is that, any Hero can beat any Hero with the right skills, aim, coordination, and practice. However, I believe the above outlined heroes are the most effective at dealing with Genji. Remember, Overwatch is a team game; while your individual skill is important to some degree, your team is there to back you up, and you're there to back up your team. Work together, make proper callouts in voicechat, and you'll be dealing with Genji in no time.

Gengi and tracer are almost the same. They are squishy assassins type characters.

So what are their counters? Something that can land a stun, prevent the assassination and kill them on the spot.

Things like Reinhart or McRee, that have an instant stun that will prevent them doing damage and mostly kill them on the spot.