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Tear Jerker: Magical Girl Lyrical Nanoha StrikerS
The scene in episode 25 with Signum and Zest.
In episode 20, where Nanoha and Vita give a speech about the upcoming battle to the forwards.
The flashback from episode 17 where Erio is told that who he thought were his family weren't and is taken away from them.
Nanoha's Near Death Experience in the flashback from episode 9. Made even more heart wrenching when they focus entirely on Nanoha as she tries to go expedite her own recovery, being in a lot of pain while trying to stand, then Shamal states at that time, her injuries may end her career and possibly cripple her for life.
When Vivio is kidnapped, Nanoha continues to perform her duties, but after a conversation with Teana, sees the stuffed bunny that she gave Vivio on the ground. One could feel Nanoha's pain upon seeing the look on her face when she's suddenly reminded of Vivio. Once she finishes and no longer has anything to keep her mind off it, she breaks down crying in Fate's arms.
Hayate, while holding a near-dead, bloody Vita with a shattered device:
"The Iron Knight Vita and the Steel Count Graf Eisen. There is nothing in this world they cannot destroy!"
Nanoha's entire scene with Vivio from episode 25. The one where Vivio is on the verge of despair and Nanoha has to bring her back from the brink.
In the third Sound Stage for this season, Reinforce Zwei finds a recording left behind by Reinforce Eins that shows her living with the Yagami family, then a message saying that this is what she gave up when she sacrificed herself, and while Eins knew it was the right decision, she regrets not being able to be with Hayate.