Heartwarming / We Must Be Killers

• Every scene where one of the mentors either treats their Victor like a biological kid while hanging out with them or helps them get over trauma or those mentees reciprocate (Brutus comforting Emory when she loses her first tribute, Misha trying to get Lyme to celebrate the holidays, etc.).
• In "Que Sera Sera", Lyme's mother thinks back about how (after being tricked into getting pregnant and married in her early teens and suffering an abusive domestic life until she left her husband), she told her second husband that she didn't want kids, and was surprised and moved when he made it clear that he respected her decision. She then looks down happily at Lyme's half-sister and thinks "Funny some of the things a person chooses when they're actually given the choice to make".
• In "Fighting for the Holidays", while Petra is mostly annoyed that the others go easy on her or avoid fighting her whenever she passes under mistletoe (due to their new village tradition) to avoid hurting her bad knee, she is touched when her Victor-sister Emory makes a formal and dignified request to serve as her champion during one potentially dangerous fight.
• One bright spot at the end of Make Us Proud, which has multiple District 2 characters thinking Was It Really Worth It? about the Rebellion (and having nuanced reasons to wonder that), is Alec observing his friend Selene's Adorably Precocious Child little brother playing and thinking about how he will never have to experience Training from Hell while preparing to be a Career or Peacekeeper.
• A District Upside Down: The War probably has as many heartwarming moments as the other stories combined. Lots of it is just how its canon divergence Fix Fic nature suddenly means that so many well-developed characters who were Doomed by Canon may no longer die (many still do, but many more live) but there are many other heartwarming moments mixed in there as well, like the affection and respect that even loyalist Peacekeepers show to the Victors from their District (often prompting a Heel–Face Turn, Mercy Lead, or other act of mercy), an avox comforting Petra after the apparent deaths of her fellow Victors, Beetee requesting to move to District 2 after the war so their therapists can help his last remaining former mentee Eibhlin, and Ronan reminiscing about his dogs and eventually being reunited with them.