This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Death Masks
Throughout the whole story of Death Masks, Marcone went through a lot of trouble to secure the Shroud of Turin. Enlisting the Churchmice, getting extorted into paying millions more for it by Valmont to make sure it's safe, even personally risking his life with Harry, Michael and Sanya to fight Nicodemus, pulling off incredible shots just so he wouldn't harm it. Near the end of the story, we learn why he went through so much trouble: he wanted it to heal a girl in a private hospital in Wisconsin. The real Tearjerker part was Gentleman Johnny Marcone, Affably Evil criminal mastermind, head of the biggest criminal empire in the country, putting a teddy bear in her arms, reading her a story out loud for an hour, laying the Shroud on her, and praying.
I hadn't ever pictured John Marcone praying. But I saw him forming the word please, over and over.
Made even more poignant after reading White Night, where we discover that the girl is the Beckitts' daughter, who has been in a coma for years after being hit by a stray bullet meant for Marcone. Marcone hasn't even told the girl's mother, who now works for him but has tried to kill him at least once, because he doesn't want to devastate her even more if the girl never wakes up. Marcone put up with all that effort, money, and personal danger in the hope of helping a little girl who was hurt because of him. Not only that, but Harry also realizes that it was that event that gave Marcone the drive necessary to because the leader he is; his taking over and organizing of Chicago's crime was less for selfish reasons, and more in order to make the crime organized so that nothing like that would happen again. Marcone might be scum, but it's hard not to like him sometimes.
Even worse, with the revelation in White Night, Fridge Logic tells us that after all the trouble and effort in Death Masks the Shroud didn't work. The Beckitts' daughter is still comatose. Imagine how that realization must have felt for Marcone.
Although it is hinted in Skin Game that the Shroud in Death Masks may be a fake, which could explain why it didn't work.
Assuming that the public-domain artifacts in the Dresden universe are identical to their real-life counterparts, the Shroud of Turin is definitely a fake.
It's fake. Harry found the real one.
The closing paragraph of Death Masks. For two entire books, Harry's been obsessed with researching a way to save his ex-girlfriend Susan, who was half-turned into a vampire. It's gotten to the point where he's almost been evicted from his office and home in his desperation to find a cure. At the end of the book, Harry finally lets go. He takes down her picture and the engagement ring he offered her from his mantle, and instead puts up the holy blade Fidelacchius, given to him by a man who surrendered himself to torture to give Harry a chance to live. The final lines, "Maybe some things just weren't meant to go together. Things like oil and water, orange juice and toothpaste. Me and Susan. But tomorrow was another day", always choke me up.
The Archive. A seven or eight year-old girl with the sum of human knowledge and endeavor stored in her mind as a safety precaution. Born to a mother who served that same purpose and who, on her birth, was burned out mentally by the passing of that knowledge to such a degree that she was put into a persistent vegetative state. A fate that she will share when, not if, she gives birth to her own daughter. Though she may seem Wise Beyond Her Years, she is still just a little girl who loves kitties and who no one thought to name beyond her function. There is something terribly sad about someone so young fulfilling such a duty.
As of a later book, this is no longer the case via retcon. Instead, the Archive passes from one to another on death of the parent. That said, it's even worse—Ivy's mother came into the Archive unexpectedly young, while pregnant with Ivy, grew insanely jealous that her daughter would have a full life that she wouldn't, and killed herself. And Ivy knows all of this.
There is a very quick throwaway line she has right when she's introduced.
Harry: Cross my heart, hope to die? The Archive: You don't know how much.