The original video performed by hitomi (under the name Minami Hokuto) that inspired Mahou Shoujo Lyrical Nanoha. It is from Triangle Heart 3: Lyrical Omocha Hako, a fandisc released on June 29, 2001, for the eroge video game Triangle Heart 3.
The CD contains a large amount of fan material, including a number of visual novel-like stories called "mini-scenarios." One of them, titled "Magical Girl Lyrical Nanoha," casts Nanoha Takamachi (a minor character in canon) as a magical girl. It serves as a prototype for the Mahou Shoujo Lyrical Nanoha anime series.