This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Blue Gender
Blue Gender is mostly an action/horror series, but this troper found himself tearing up when Yuji is being driven mad by his overactive B-cells and Marlene is trying to talk to him and bring him back to his senses. The way Marlene speaks, suggesting that she knows she's in danger of losing the only person who matters to her, is especially poignant.
Even though they're borderline bad guys for much of the series, Su and Lu's great big hug on finding each other still alive qualifies.