His first appearance at the end of season two had him paired up with Ben, and the two took on the stereotypical roles of disappointed parents; while Ben was the disapproving father, Chris took the supportive, positive mother type to new heights, bubbling with enthusiasm and deferring to Ben when things got more difficult to discuss. Again, while the show could have just stuck with this formula, the writers revealed that it was more of a survival thing based on the characters' respective personalities. While Chris was literally addicted to positivity - more on that later - Ben was so focused on succeeding because of Ice Town, and because of that, neither was able to accomplish anything. Ben and Chris' strengths made up for their weaknesses, and they successfully saved several Indiana cities from bankruptcy, ultimately ending up in Pawnee where they both meet their significant others.
I think I mentioned this in the actual challenge, but Chris' ability to cry - and be vulnerable, in general - was so refreshing to see, and he brought that out in others. Well, not Ron, but that's Ron. He will openly weep at beautiful words and touching gestures, he discusses his own struggles with depression and anxiety with inspirational honesty, and he is genuinely thankful of any compliments, coming from any gender, instead of becoming weird or defensive. I didn't exactly click with Chris like I did with the other characters** at first, and it wasn't until after Millie Gergich broke up with him that he finally seemed like an actual person. Hearing Chris' backstory - he wasn't supposed to live as a child due to a blood disorder - did frame his positive attitude better, but then the show went and looked at it in a different light: Chris suffered from mental illness.
* Politics aside, I just get a skeevy feeling from him, which goes back to his having sex with a 16-year-old back in the 80s.
** This does not include Mark. Because fuck Mark.