These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Tear Jerker: There's a lot of them. Several of Yukiko's arguments with her father qualify. Especially A Reason You Suck Speech she gave out to him before saying, "I hate you." She even felt sadness when she remembered it.
Her backstory is also depressing. She lost her dog and twin brother at a young age.