Downplayed: Markus, Hiro, and their friends are all goths and hate preps. Because they're teenagers, they consider it to be very Serious Business. One day Markus comes to school in a pink polo with a popped collar and starts hanging with the preps, participates in their teasing of goths, and tells them some of his friends' secrets. When he realizes that's just not him, his goth friends give him the silent treatment for a couple days, then forgive him and invite him back into their clique.
Justified: Markus has skills they need to take down The Empire.
Subverted: Hiro and the rest of the party take Markus back... then turn him over to the authorities at their earliest convenience or if that's not possible, beat the tar out of him and leave him by the side of the road.
Double Subverted: Hiro leaves Markus on his own after refusing entrance to the team... but returns later, usually in a Big Damn Heroes moment, to accept him anyway.
Parodied: Markus backstabs Hiro, then apologizes. The team takes him back. Markus backstabs him again, then apologizes. The team takes him back. Wash, rinse, repeat. Bonus points if Markus looks like Gríma Wormtongue.
Zig Zagged: Hiro and Sarah forgive Markus immediately, but Nathan, Candy and Buck don't, while Blaze and Wendy aren't sure what to think.
Averted: Markus doesn't want to come back, nor does Hiro ask him.
Lampshaded: Hiro: "Markus, I welcome you back because that's what heroes do. We forgive people. Now let's see if you can keep that forgiveness."
Invoked: Hiro's first impulse isn't to welcome Markus back, but he's trying to be a better hero so he does it anyway.
Exploited: Markus felt safe betraying Hiro because he knew he'd be accepted back into the fold if his Face-Heel Turn went pear-shaped.
Defied: Hiro: "Markus, I should let you rejoin us. I should forgive you, as it is the way of a hero... But I will never forgive you, you backstabbing weasel!"
Deconstructed: Markus's actions — and the way the heroes accepted him back so easily — reflect poorly on the party as a whole. Civilians who heard of his misdeeds distrust the team and are much less willing to help them out. Emperor Evulz takes advantage of this by claiming Markus was still working for him during a key battle, distracting the team with new waves of suspicion and distrust.
Reconstructed: After being Easily Forgiven, Markus works to prove himself worthy of that trust and becomes a faithful, loyal companion.