Ellie Kemper's turn as Erin Hannon, the receptionist who replaces Pam at Dunder Mifflin after Pam leaves for the Michael Scott Paper Company, was perhaps the last truly great series regulars added by The Office. Yes, there were some fun additions in later seasons (Clark ended up turning out fun when the show stripped him of his sleaziness), but Erin seems to be the last one in the door.
Immediately carving out a niche of weirdness for herself on the show, Erin was also grounded in the reality of Scranton, despite the fact that she occasionally seemed more heightened than others. As such, she was afforded the opportunity to forge bonds with her coworkers, some of which are clearly meant to be transcendent of the workplace in their strength.
Gabe
In spite of how her relationship with Gabe ended up (since Erin implored he stop talking to her forever), her relationship with him has to be among the strongest she made in the office.
After all, despite the frequency which saw many of the characters dated one another in Scranton, Pennsylvania, some relationships still managed to have long tenures. Erin and Gabe lasted for almost the entirety of season seven, meaning some connections and tethers were built, even if they were never meant to last forever.
Kevin
While Erin really only dated three men from Dunder Mifflin, her boss, Michael Scott, did his best to set her up with one of his three best accountants, Kevin.
A relationship between Erin and Kevin may not have worked out, but Erin still went to great lengths to be friends with Kevin. They eventually bonded over their shared dimness and ingenuity, showing friendships can be maintained even when dating fails.
Pam
Could one say that Pam and Erin were ever truly friends? Perhaps not. It can be tricky to be friends with one's replacement, especially when Pam did attempt to get her job back from Charles Miner.
Yet, there are still shades of a mentor-based relationship between Pam and Erin. Pam has wisdom about the office's front desk and the procedure for answering phones. Erin may not always take it, but it's clear that she has reverence for her predecessor.
Kelly
The closest thing Erin had to an actual friend on The Office was definitely Kelly. Some of their friendship was developed in online web videos like "Subtle Sexuality," but they were also shown to hang out with one another during the show as well.
They are both youthful characters who are oriented, occasionally, towards more superficial things. Kelly definitely brings that out more in Erin, though, considering Erin is often unaware of how poorly Kelly occasionally treats her. At least they share the same first name, though.
Dwight
When Dwight is finally named the new regional manager in the last arc of The Office, during season nine, it is Erin who celebrates just as loudly as Dwight does. She fist pumps and shrieks in joy from the receptionist desk and is truly happy for Dwight, who has become her friend.
Over the course of the show, Dwight also softened towards Erin. While he initially tried to court her, the loyalty he brings to any friendship resulted in a strong between the two oddballs.
Darryl
Towards the later seasons of The Office, character groupings began to break off into something resembling cliques. The accountants received their own story arcs, Jim, Pam, and Dwight formed a trinity. And Andy, Darryl, and Erin found friendship storylines between themselves, as well.
As such, it's Erin who pushes the hardest for friendship resolution and closure after Darryl attempts an Irish goodbye from the office, en route to Philadelphia. (She also enjoys being "sneaky sneaks" with him before he commits to Athlead full time.) It may be a 70/30 friendship dynamic between the two, but Erin has enough love for the both of them.
Phyllis
There was a time in season seven when it seemed like Erin might actually be the birth daughter of Phyllis, who gave away a child in her younger years. It ultimately ends up not being the case, but the possibility of it provides a strong bond between the two all the same.
When Erin eventually finds her birth parents in the series finale of The Office, the camera lingers on Phyllis for a moment, showing her choked up. She's truly happy for Erin because even if she's not her birth mother, there's still clearly a bond between them.
Andy
The camera also lingers on Andy in this moment. Even though their relationship ended unceremoniously, the two still wanted the best for one another. It's a shame that their relationship never got the timing right on the show, as they both were so charming with one another.
The season six to the middle of season eight arc of Andy is the character's best and that's when his relationship with Erin is at its strongest. Even though things ended between them with tumult, they will always share a connection and care for one another.
Michael
In "Goodbye, Michael," the staff members of Dunder Mifflin each get a moment with their departing Regional Manager. Some get big moments (Jim, Pam, Dwight). Others get rushed moments (Meredith, Creed, Gabe). Erin, however, received a heartfelt talk with her boss, whom she clearly projected father figure feelings onto.
Michael was confused and reluctant about this at first, but by the time he left Scranton for Colorado, he understood the bond he had with Erin and how much it meant to her. There is no one Erin sought pride from more than Michael on The Office.
Pete
While Erin did not make it with either Andy or Gabe, she does have a solid relationship with Pete. A measured, calm, supportive personality, Pete is clearly the one for Erin. He's the only one of the three who prioritized her safety and happiness over his own.
In the last shots of The Office, Erin and Pete are seen together, implying that they find their own happily ever after with one another. That's for the best because her connection with Pete is clearly the strongest relationship Erin had on the show. And the writers pulled off that arc in just one season.