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Tear Jerker: Katamari Damacy
The ending credits of the first Katamari Damacy, of all things. It's gotta be the ending song, Katamari of Love... it's so cheesy, but it's such a pure expression of hope...
In the last flashback of the We ♥ Katamari game, the flashback is of The Prince's birth and how happy his father is. Either you'll cry at how beautiful and emotional the scene is, or you'll cry at the fact that now he doesn't even remember which of the cousins he is, and how he constantly makes fun of him.
The King of All Cosmos' backstory. The part where the King's father fishes the second-place trophy out of the river showed that despite his strict attitude, he really cared about his son. When the young King runs to his father in tears, you can almost imagine him saying, "I'm sorry, father!" and his father replying, "I'm sorry too, son."
The very first cutscene reveals just how hard the Emperor pushed his son, leading to uncomfortable implications about the King repeating the cycle with the Prince. Even after living through all of that firsthand and knowing how badly it screwed him up, he still treats his son like The Unfavorite and acts like he doesn't even remember him at times...
Katamari Forever: after the King wakes up, the RoboKing's anxiety kicks into overdrive: what's the point of having a Replacement Goldfish once the original comes back? Then the King learns about him, and is absolutely furious, ordering you to dismantle him at once. You have no choice but to roll him up as he lies there helplessly, piece by piece. The happy, cheery ending sequence feels pretty darn dissonant for anyone who liked the poor RoboKing.