One of the saddest deaths in anime is from the series "Clannad: After Story," specifically the death of Nagisa Furukawa. This anime is known for its emotional storytelling and poignant themes. Without giving away too many spoilers, Nagisa's death is a heart-wrenching moment that deeply affects the viewers and the protagonist, Tomoya Okazaki. The series explores themes of love, family, and the impact of loss, making it a memorable and tear-jerking moment for many anime fans.
Keep in mind that there are numerous other anime with impactful and sad deaths, and individual opinions may vary depending on personal preferences and emotional connections to the characters. Anime often deals with a wide range of emotions and can be quite powerful in evoking feelings in its audience.