Heartwarming / The Little Mermaid

The original tale

• The mermaid's sisters try to rescue her life by giving her a knife to kill the prince. She decides to kill herself over killing him.

The Anime

• Duke the Whale agreeing to take Marina to the surface.
• Fritz saving Marina from the polyps.
• All of her sisters cut off their hair in exchange for a knife that can save their little sister.
• Marina refusing to kill the man she loves and dying with dignity.
• Marina obtaining a soul and going to Heaven when she dies.

The Disney film

See here.