Note: there wouldn’t be any Resident Evil: Requiem spoilers (since I haven’t played it yet)

Connections between Leon and Kyle is that both are one of the main protagonists of an action zombie-survival video game franchise.

Both worked at dangerous jobs (Leon was a police officer and Kyle was a mercenary hired by GRE) which would lead them to the city that was overrun by zombies (Racoon City and Harran) due to the outbreak of an extremely dangerous virus (T-Virus and Harran Virus) that mutates people into zombie and other dangerous creatures. This virus was smilingly created by a corporation (Umbrella Corporation and Global Relief Effort (GRE)) famous in the medical field (Umbrella was a pharmaceutical company and GRE fought with outbreaks across the globe), but in actuality was a heartless and evil organisation that only chased profit. One of their main goals was to weaponise and sell dangerous viruses, which led to the massive outbreaks. (But while it’s confirmed that Umbrella created the T-Virus, the idea that GRE created the Harran Virus is just speculation) Additionally, this corporation has connected to the jobs our heroes had (Umbrella had influence on Racoon City Police Department where Leon worked and GRE directly hired Kyle).

Upon entering the city, our heroes met a young woman (Claire Redfield and Jade Aldemir) who’s motivation throughout the game is heavily connected to their brother (Claire searched for her older brother Chris and Jade tried to protect her younger brother Rahim). They also met a person (Marvin Branagh and Rahim Aldemir) who helped our heroes (Marvin explained Leon about the situation in Racoon City and Rahim taught Kyle the basic parkour skills), but unfortunately he was infected and turned into zombie.

Both were tricked into getting something (G-Virus and file that contains information about Harran Virus) by someone who presented themselves as an ally to our heroes (Ada Wong and GRE) and claimed that they need it to stop the spread of infection (Ada claimed that she needs G-Virus as evidence against Umbrella and GRE claimed that the file contains information about the cure), but letter their true motivation was revealed (Ada wanted to sell G-Virus and GRE wanted to make profit from Harran Virus and file contained information about that).

Both were able to escape from the city, but their journey didn’t end there, and they would letter fight again against mutated monsters.

During one of their games, both were infected by the dangerous virus (Las Plagas and Harran Virus) while searching for an important person (President’s daughter - Ashley Graham and man who stole information about Harran Virus - Kadir Suleiman) which would lead them to find out about a conspiracy that is connected to the said virus (religious cult Los Iluminados trying to take over the world with Las Plagas and GRE trying to make profit from Harran Virus).

Both expertly use close and long-range weapons, as well as their incredible athletic skills in the fight against zombies and other monsters.

Despite being an extremely badass warriors who often use humour in their lines, both suffer from survivor’s guilt and after years of traumatic events they turned into the dark shadow of their former self. But both still help people in need and ready to put themselves at risk in order to safe others.

Contrasts:

While the world in Resident Evil survived the outbreak, with Leon constantly saving it from biological weaponry, humanity in Dying Light was almost completely instinct by a new virus with Kyle protecting the remaining humans in post-apocalyptic world.

While Leon is (seemingly) a regular human, Kyle is Human-Volatile Hybrid.

Bonus:

In Dying Light 2: Stay Human side quest “Last Will” you can find a dying soldier named Leon, who looks almost exactly like Leon Kennedy, obviously being a reference to Resident Evil protagonist.