You can start by looking on Archive of Our Own (AO3). It has a vast collection of fanfiction for all kinds of pairings, including mccree x hanzo. The site has a great search function that allows you to filter by tags, ratings, and word count.
Some Tumblr blogs are dedicated to Overwatch fanfiction as well. You can search for mccree x hanzo fanfiction on Tumblr using relevant tags. Just be aware that the quality and length of the stories can vary greatly, but it can be a fun place to discover some unique takes on this pairing.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions including many for the mccree x sombra pairing. The website has a great search function that allows you to filter by tags, ratings, etc.
There's this fanfic called 'A New Alliance'. It's not just about the relationship between Hanzo and McCree but also about how they team up to face challenges in the Overwatch world. The way the author writes their interactions is quite engaging.
One great mccree x hanzo fanfiction could be 'The Meeting on the Bridge'. It beautifully depicts their first encounter and the initial sparks of an unexpected friendship. The story focuses on how their different personalities, McCree's laid - back cowboy nature and Hanzo's more reserved samurai - like demeanor, start to complement each other.
One common theme is redemption. McCree and Hanzo both have complex pasts, and many fanfictions explore how they find redemption through their relationship. Another theme is trust. Since they come from different backgrounds in the Overwatch world, building trust is a big part of their stories.
Fanfiction.net might also have some. Although the interface is a bit old - fashioned, it still hosts a decent amount of Overwatch - related fanfictions. Just be sure to use the search function properly to narrow down your results to what you're looking for.
The plot is key. It could be something as simple as them getting to know each other better during a mission or a more complex story about their pasts affecting their relationship. Also, the chemistry between them has to be believable. If it feels forced, the fanfic won't be good.
A common theme is the clash and then the melding of their different cultures. McCree represents the wild west sort of cowboy culture, while Hanzo has his traditional Japanese heritage. Their fanfics often explore how these two different worlds come together.
One popular 'Overwatch McCree x Hanzo fanfiction' is 'The Road to Redemption'. It beautifully explores their relationship as they overcome past differences and fight together. Another great one is 'A New Bond' which focuses on how they gradually develop feelings for each other during a mission.
You can try some popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of Overwatch fanfictions, including those about Hanzo and Mercy. Just search for 'hanzo x mercy' in the search bar, and you'll get a list of relevant stories.
There's 'The Path to Redemption' where Hanzo is on a journey of self - discovery and McCree becomes an unexpected part of it. This fanfic shows their growing connection in a very heartwarming way. It has some really nice dialogue exchanges that bring out their chemistry.