The fact that although Jack and Rebecca lost the third triplet, they chose to give an abandoned Randall a home and raised the baby as their own.
Kate's beating down on herself and begs her brother to yell at her. Kevin refuses and subtly directs her to give herself the Tough Love speech.
Kevin's drunk and lamenting that he just torched his acting career, and Kate reassures him that he'll bounce back.
After plenty of tension over how Randall will reveal to his family that he found his biological father, he quickly tells Kevin the truth when he makes a surprise visit. And for his part, William is thrilled to meet the star of a show he loves.
The entire Thanksgiving episode, showing how a disastrous Thanksgiving from the siblings' childhood became a bunch of family traditions for the holiday, culminating in Kevin finally allowing his stepfather to take part in them.
As part of Randall's inclusion into a judo class just for black children, Jack is asked to do pushups with Randall on his back. He does so and continues to do so even after asked to stop. After the episode aired, Milo Ventimiglia, Sterling K. Brown, and Justin Hartley posted on their Twitter accounts of them doing push ups with each other on their backs.
How nonchalant this went.
Tess: Dad, Grandpa's gay. Or at least bi.
In the Thanksgiving episode, William telling Olivia that when someone who clearly adores you offers you pie, you accept. (It Makes Sense in Context.) Too bad it doesn't stick.
Kevin saving Sloane's play by convincing her she can act in it.
It's small, but William saying he wouldn't trust Jesse's opinion while out shopping, because in his words, "he thinks I look good in everything."
Kevin abandoning the play so he can be there for Randall when the latter suffers a nervous and emotional breakdown. The way he just sits there, holding his brother and comforting him is just incredibly moving, particularly since the two never had a close relationship in the past.
William paying his respects to his son's father at Jack's grave - his favorite tree - in "Memphis."
Randall's dream that he tells Kate about William and Jack meeting and talking about the time they had with their son together. It just shows and reinforces that in the short months he was with him, Randall had accepted William as his father also.
Beth is saddened that William seemingly left her nothing to remember him by until later near the end where Beth discovers a postcard from Memphis that William had sent her while he and Randall were on the road. Tears of happiness and joy come from her eyes.
Randall forgiving his mother for hiding William from him all these years.
What gave Jack the strength to kick his drinking habit the first time? Assurance from little Kate that everything was gonna be alright note that she uses the same technique Jack used to calm Randall when his anxiety would kick in.
Teenage Randall secretly arranges to meet his birth parents. When Kevin and Kate find out, they accompany him to the meeting spot. The (white) woman who shows up appears to be a junkie and is clearly looking for money so Randall storms off. Kevin and Kate later come to check on Randall and make sure hes okay. Given that Randall has always been the odd man out with Kate and Kevin being twins and weve already seen that Kevin and Randall never got along very well, its really sweet that the twins were there for their brother when he needed them.
In Brothers Jack takes Kevin and Randall on a camping trip to help them bond more during the episode we see Randall writing in a notepad presumably on what to do during the camp trip. Later when Kevin looks at it it turns out he is writing down all the ways to get Kevin to like him and get on his good side and with this we see the rare moment of the brothers bonding together as children.
10-year-old Kevin giving all his Halloween candy to the boy Kate likes in "The 20s" so that the boy will hold her hand in the Haunted House.
Charlotte mailing back Kevin's necklace which he thought he lost at her house. Kevins face alone just tells you how overjoyed and grateful he is to have the last reminder of his father back.
Jack going full on Papa Wolf at the beginning of Super Bowl Sunday the minute he sees the house on fire he wakes his wife makes sure to ask Rebecca if Kevin is indeed not home and safe, rescues Randall, then saves Kate by using her bed as a shield for her ( and getting burned himself in the process by the flames) just the utter love and protectiveness he showed for his family is just incredible to see.
Rebecca getting her yearly laugh from Jack in the form of Kevin, joking that in his effort to make amends with his father, he might have spoken to the wrong tree.
The final twist in "Super Bowl Sunday" that an adult Tess is now a social worker helping kids find foster families, having been inspired by the family's experience with Deja.
Vegas, Baby shines light and more depth on the relationship of Kate and Randall and reveals that after Jacks death the two grew closer with Kate even stating her fear growing up was knowing that she was going to lose him. Randall himself assurers her that she will never lose him and even reveals all those times he watched Sex and The City with her as teenagers was just because he knew she liked the show.
Kate and Beth bond after an intense argument between them involving Randall with the two confiding in each other over their flaws and issues.
Toby is enthusiastic to hang out with Randall and Kevin during their bachelor party in Vegas. Why? because he sees them as his brothers after stating his younger brother who is a decade younger then him isnt really close with him.
Young Randall passing on attending Howard University for the fall. Why? Because his mother and his siblings need him.
Jack's grandfather is revealed to be an alcoholic and distant from his son, who continued the pattern and made it worse with his active abuse. This makes it quite retroactively touching that despite his own issues with drinking, Jack was able to break the cycle and be a good husband and father.
The Reveal of where Jack learned the breathe technique he used to help calm Randall during his anxiety attacks: A war buddy from Vietnam named Donny who sadly lost his foot stepping on a mine and was sent home as a result. His advice to Jack? Just remember to breathe when it all gets to much.
Circumstances force Kate to be the one to guide Tess through her first period, which gets Tess to trust her enough to come out of the closet for the first time. Kate in turn promises not to tell anyone else, while encouraging her that her parents will love her no matter what, while we've already seen that she and Randall are still close in the future.
The season ends with the clearest look yet into the future timeline, and despite the major reveal of Rebecca's severe dementia in her old age, it's also very comforting for the most part: Randall and Beth are still happily married despite their difficulties over the season, Kevin has a son like he always wanted, Kate's son Jack survived his premature birth and seems to be healthy, and Nicky has become a lot closer to the rest of his family.
The entire reveal that regardless of any drama that may surround him in future episodes and despite his blindness, Jack Damon becomes a happy, well-adjusted adult who even finds the success in his singing career that his mother and grandmother never did.
Deja immediately gets a crush on Malik, resulting in her coming home with a beaming smile that has Randall asking if something's wrong with her face.
Jack makes a small mistake on the paperwork of a deal that causes his company to lose $20,000. Despite 20 years of service, his boss is going to fire Jack for this. As soon as he hears this, Miguel marches into the office and tells their boss that if Jack goes, so does he and all the clients that bring in major money for the firm. Later that night, Jack calls up Miguel to tell how much it meant to put his own career on the line for him and how the man is his best friend. While he tries to laugh it off, Miguel is clearly touched by Jack's words.
A meta one: With Timothy Omundson wanting to get back into acting two years after a major stroke despite his continued physical disabilities, the show created a recurring role specifically for him designed around his new limitations to get him back in the market.