Episode 12 basically, especially the last few minutes. Nice things happen for a change in an otherwise screwed up world.
The abrasive and somewhat Jerk Ass Hitagi admitting to Araragi that she's in love with him. Also the reason why she fell in love with him: his willingness to help her out with her problem despite barely knowing her (and her violently trying to discourage him), and the fact that he found nothing exceptional about this: Araragi assumed that anyone would act as he had in the Hitagi Crab story arc.
From Nekomonogatari: White, after Hanekawa's house is burned down she decides to stay at the abandoned school Oshino used to live in (she later admits she was probably so shocked from losing the house that she wasn't thinking clearly). Come very early next morning and Senjougahara frantically wakes Hanekawa, having spent the entire night searching the town for her. This is also one of the very few times in the series where we ever see Senjougahara really lose her cool.
The entirety of Koimonogatari is pretty much a punch in the heart, most of which are delivered by a previously-thought-to-be-evil Kaiki Deishu.
Kaiki, in a roundabout way, agrees to help Senjougahara deceive Nadeko and stop her from killing Araragi, Shinobu and Senjougahara for much less than he was originally planning to charge because he genuinely wants to help her.
Senjougahara admitting without second thought that she would rather save Araragi's life than her own if she had to choose, and would even sell her own body in order to make the money needed to do so despite her traumatizing past.
After Kaiki tells Senjougahara that Araragi's life will be spared from Nadeko's wrath, Senjougahara, who had up until that point had been mostly extremely cold and abrasive towards the man, gets up to leave for the bathroom and comes back minutes later fresh from crying from relief to give him an uncharacteristically heart-wrenching and sincere thanks.
Kaiki (again, in a roundabout way) confirms that he conned Senjougahara's parents in order to separate the girl from the mother that caused her so much pain and then later conned the cult Senjougahara's mother joined into collapsing in an attempt to enact revenge on Senjougahara's behalf and reunite her with her mom, although both acts backfired on him.
The speech Kaiki delivers to Snake God Nadeko in order to convince her to give up godhood. One part a good scolding and two parts... actually pretty inspiring: he tells her that the goals and talents she has are not embarrassing, convinces her that she's worth much more than Araragi's affection and pleads for her to try different things in life in order to find happiness. All things she can only do as a human. And it works.
The theme song of Hanamonogatari plays with a montage of Kanbaru and Numachi being happy together in middle school before showing a fight and Numachi's broken leg as she's sobbing in the rain, the dissolution of her basketball career and a slew of other issues culminating in her suicide as mentioned in the story. When Kanbaru encounters her in the present, Numachi herself had become a misfortune-collecting oddity who did not realize she was dead. In the aftermath of their final basketball match Kanbaru and Numachi laugh together again, Numachi finally finds peace, and she ascends as a spirit.