Ragnarok: the Animation has one such moment when Alice, Maya's friend, is forced to become a monster and Maya-chan kills her with her own hands before realizing who she is. The subsequent episode is a tear-jerking episode after Maya realizes what she's done and apologizes to the already dead Alice.
What makes it worse is that during poor Alice's transformation it's clearly in pain/doesn't want to be a monster Maya may had not liked it but by killing Alice, she put her out of her misery.
Jiltus' act of Taking the Bullet for Maya inflicts serious injuries to her. Despite that, she manages to use her last strength to conjure a barrier that protects Maya and Poi-Poi from Zephyr's Lord of Vermillion, which results in her death. This leaves a heartbroken Maya behind.
Keough's final farewell to Yuufa in episode 26. All of it.
This part is extremely heartbreaking:
Yuufa: Where are you going, Nii-san?
Keough: Yuufa, I can no longer be with you, from now on, stay with Roan. He will protect you... indefinitely.
Maya leading the group to a lair of ants in episode 9. It's fairly mundane but peaceful since the ants are minding their own business. They even watch a queen ant lay an egg which will eventually grow into a new queen. Then Takius decides to destroy said egg, which earns the group the wrath of the entire colony, and they're forced to kill the queen after she blocks their escape path. In the end almost everyone in the group does a collective What the Hell, Hero? to Takius.
