This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Tenchi Muyo!
In Universe, Ryouko is mortally wounded and keeps it a secret from Tenchi (even when hugging him goodbye), flies him into Jurai's defence zone, drops him off at the palace, but cannot go on due to blood loss. She pretends she won't go to rescue Aeka with Tenchi and leaves in her ship. Later she dies of blood loss in the cockpit with an odd smile... I shed manly tears.
During the "Dark Washu" arc of the Shin Tenchi Muyo manga, the titular character gets Hijacked By Doctor Clay and becomes a villain, forcing Washu into a Sadistic Choice: brainwash the others into forgetting her and face her Evil Counterpart alone, or see them get repeatedly attacked. Washu chooses to wipe the others' memory, despite Tenchi being right there when she makes the decision and begging her not to go through with it.
This leads to another painful moment when Minagi runs into Washu and Ryo-Ohki, who ignore her and she runs off to tell the others, only to find out that they have no idea who Minagi's talking about. She's quite distraught that they forgot about Washu until they start thinking harder.