Shirogane finding a crying Kaguya in chapter 45 and then taking her to finally see some fireworks.
Shirogane's father managing to get a confession out of Kaguya with a single conversation after he had been unable to do so in 86 chapters.
Ishigami at the end of chapter 89. Three words: "Shut up, stupid."
Kaguya did end up telling someone about Ishigami's incident— the ruthless VIPs mentioned earlier back in the series—and the narrative all but states Ogino transferred schools because of them. Looks like karma was delivered to the right person after all.
Shirogane's Grand Romantic Gesture in the culture festival. He made sure to arrange the festival events to get Ishigami and Iino busy, set up a Gentleman Thief mystery to get Fujiwara out of the way, and stole all the heart balloons in the school. All so he could set up a shower of hearts for Kaguya and ask her out to Stanford together. What made this even more awesome is what Kaguya gave as her reply.
Mere hours after the anime's 12th episode (adapting chapters 44 to 46), the discussion thread on Reddit was being gilded at record speed. Within a day, it has become the most gilded thread in Reddit's entirety. The community knows no bounds in showing their appreciation for the series.