After Rikka is hit with the fact that her father is dead, we can't see how she is going to react, because the half of her face we are shown is obscured by her eyepatch. Then a tear rolls down.
Episode 11, full stop. Everything from the beginning where Touka leaves for Italy to Dekomori's distraught reaction to Rikka's rejection of chuunibyou; it kind of makes you feel for a minute what it's like to lose someone you generally look up to, even with how rich and intelligent someone like Dekomori is.
A particularly notable tearjerker comes from Rikka announcing that the club will be disbanded. Dekomori breaks down at the realization of this and has to be dragged out of the clubroom and subsequently comforted by Nibutani.
Yuuta subsequently breaks down as a result as well.
Rikka finally accepting her father's death.
Rikka: Goodbye, Papa.
What Nibutani has to go through in Season 2, Episode 8: Not only has someone takes over her "Mori Summer" identity but Dekomori seemingly fallen for it and accepts this impostor over her. No matter how akward and tense her relationship with Dekomori is, Nibutani is heartbroken and just leaves in defeat to continue her school life.