Chapter 3, the flashback where Lelouch recruits Shirley. the poor girl has a case of Driven to Suicide and throws herself off a cliff. Lelouch uses his dragonslayer magic to save her and then tells her that her gift is real because she had lost her faith in her ability as a magus.
Chapter 9 where Marianne tells Kallen that she’s home.
Chapter 15 where Marianne calms Cornelia down while she’s having post-victory Heroic BSOD regarding the death of Estellise.
Chapter 26: The Reveal that Selina is Suzaku’s Missing Mom. She only didn’t tell him because of how differentthey are. She also abandoned him to Genbu because she believed he’d grow up better as a human being under his father than with her. She also believes that while she’s made many mistakes in her life that Suzaku was the only thing she ever did right.
Chapter 27: All of the flashbacks to Lelouch and Erza’s past history are this
Chapter 31: When Kallen starts to angst about Kraken’s Eye since it was the first guild she was ever in, it's natural to think that we’re about to get a repeat of her treatment by Iron Star. However, not only are both Kasumi and Kalina genuinely happy to see her and hear that she’s doing well, but Kasumi even apologizes for kicking her out. The guild has a much firmer grip on wanton destruction and policy violation so to find out that they did want Kallen to stay and are glad she finally found a good fit brings a smile to your face as much as it does Kallen’s. What really sells it is Kasumi giving her a big "welcome back" hug.
Chapter 35: Mirajane tells Kallen she can always rely on her as an older sister, reminding Kallen of Naoto, but also, possibly filling a void in Mirajane's heart regarding Lisanna, considering when the scene takes place in continuity.
Chapter 39: Elfman and Mirajane's heart to heart moment regarding Mirajane being asked to go on the dangerous assignment.
Chapter 41: For NaLu shippers, seeing Natsu break through the floor to punch the ever loving afterlife out of a wraith because it gave Lucy a Jump Scare can only be seen as heartwarming Ship Tease.
We get more of this in chapter 42 with Natsu giving Lucy a hug telling her he won't let her become a werwolf.