It's subtle, but Overkill has the relationship between Isaac and G. They start off on rocky terms—as an Establishing Character Moment, Isaac's first words to G are "What's up, motherfucker?!" The first few chapters are punctuated with Isaac badmouthing G and G making snarky, sarcastic responses. But they slowly warm up to each other, working together to stop the mutant outbreak as well as avenge the death of Isaac's father, and by the final chapter, Isaac proudly proclaims that G's name "stands for 'genocide', motherfucker!" and G realizes that Isaac, underneath his macho exterior and constant foulmouthing of everyone, truly likes him as a friend. The final shot before the game ends is the pilot of the rescue helicopter they're on being revealed to be a mutant, and what do Isaac and G do? They grab their guns and fire away, in unison.
In the special addition for 4, after the end of each game there is a 'Partner Rating' to judge how well the two players cooperated with each other. If you managed to get a very high score, this◊ will be the message that you get.
As long as there are couples like you in this world, there will always be hope for us all.