This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Kuroshitsuji
The deaths of Lau and Abberline in episode 20.
The very beginning of episode 22 is pretty sad, too. Maria, Abberline's to-be wife, reads about his death and gets a handful of toys as compensation. Poor Maria...
Freckles. Freckles, Freckles, Freckles. Dear God. Freckles. After that particular piece of nastiness, Ciel's grasps at redemption were pretty sad to see. "Would you like an orange, sir?"
In chapter 44, watching Maylene and Finnian's breakdown after it seems to seriously and completely dawn on them that Sebastian is dead is utterly heartbreaking. Luckily, Sebastian is not really dead.
Episode's 7 and 8 of the second season in which Alois, who before seemed like a complete jackass, is stabbed and ignored by Claude for a bit who's busy practically orgasming over the taste of Ciel's blood. Alois's tearful response "Oh, you look like you've seen a bunch of maggots squirming in a dung pile" to Claude's indifference towards him, we learn his backstory where his little brother died and left him alone, and he practically confesses his love for Claude, telling him he's the only one he has left in the world, before Claude tenderly holds his face and stabs him to death.
Episode 11 Alois(in Ciel's Body) asking Hannah to tell him that she loves him and give him a hug. Which he's ALWAYS NEEDED. She does both, which prompts him to cry tears of joy and say "Love is...warm, isn't it?" *sniff* Pass the tissues please.
Madame Red's death at the chainsaw of Grell, and Ciel's reaction. "Red is... your favorite color". SOB.
Madame Red's funeral. The red dress and the rose petals... good God! *sniffle*
The house servants having to put down poor Pluto.
How is Bird, the second series' ending theme, not on here?
The ending of the Green Witch arc: As they're getting Sullivan away, Wolf runs up to the getaway vehicle aiming his gun... to shoot the soldier trying to shoot Sullivan. He then tries to run after the vehicle still, apologizing for everything he's done to her and stating that she doesn't have to forgive him and ultimately tell her she's not a witch but a normal girl.