This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Plankton's Eye View
It's hard not to feel sorry for Plankton here. For the duration of the first few chapters, he often reminisces on his old friendship with Mr. Krabs. This is often interspersed between fits of anger and sad narrations of his past.
In reality, I'm just an unattractive, puny little protozoan with one big, red eye on his forehead. The years have painted unsightly liver spots and wrinkles on my face. (Chapter 2)
Aside from that, there are also posters of a musical where Squidward and Squilliam are collaborating. A sudden, bitter reminiscence came through my mind as I saw that after all these years, Squidward and Squilliam, who were once rivals, are now best friends. I was sure about this because I just heard a couple talking about this musical on a park bench, and they were both surprised that those two have finally gotten along because the mere prospect of that seemed impossible. I remembered that wretched crustacean, Mr. Eugene Krabs, who stole my life away from me. We were once friends that seemed inseparable. We stood by each other since our times in the nursery through the most difficult of times. We were both the school outcasts because Mr. Krabs was very poor and I was a nerd, but that was okay because we had each other. While he finished my battles for me, I finished his science homework for him and even shared my sandwich with him while enjoying the pungent aroma of the dumpster every recess time. (Chapter 3)
I went into the room where Karen is supposed to be and instead, I saw a broken monitor that is lopsided on the wall, as if it will fall off in just a few more days' time. Tears filled my eye as I saw the sight of her completely ruined beyond repair. (Chapter 3)
All of Karen's letter.
The very last author's note of the fanfic. Word of God says that the fanfic is dedicated to his grandmother. By the time he completed his fanfic, she has already passed away.