This one hit hard.
My dad found two kittens (one pure black, one pure white) buried alive not too far from our country house and we took them in. My dad spend many sleepless nights feeding them, taking them everywhere with him (we could not let them stay at our flat in the city because my sister has a cat allergy). Unfortunately, despite our best efforts the black kitten passed away a week later. The white one survived and stayed with us in our country house. At one point we weren't sure if this kitten was a cat at all — he grew very fast and had really long legs, even the vet was surprised. He also scared every other cat in the area (despite being, at the time, a week old). He was a crazy cat, wasn't scared of anyone or anything.
Then one day he was run over by a car (probably some asshole who wouldn't slow down even though there was a speed limit of 5 km/h) and passed away...