Mechagodzilla's nickname is Kiryu, which means machine dragon or mechanized dragon.
In Dr. Yuhara's first scene, he is showcasing a mechanical Trilobite and then is asked to help construct Kiryu from the first Godzilla's bones not long after. In Godzilla - Das Original (1954) a Trilobite was discovered in the first Godzilla's footprints.
Toho continued the practice of casting actors from the original Godzilla series into this series. For this film, Kumi Mizuno was cast as the outgoing Prime Minister.
Famed Japanese baseball player Hideki Matsui, a member of the New York Yankees from 2003 to 2010 and a member of the Los Angeles Angels since 2010, appears as himself. He hits a massive home run as Kiryu is flown toward Godzilla for the first time and helps a group of children get to a safe place during the sequence when Shinagawa's population is evacuated to make room for the fighting monsters. Matsui's nickname in Japan is Gojira (Godzilla).
Like the other films in Toho's Millennium Series, this was intended to be a standalone film. After production had completed, director Masaaki Tezuka was approached by producer Shogo Tomiyama to make another film. While reluctant to do so, Tezuka eventually agreed and it was filmed the next year as Godzilla - Tokyo SOS (2003). Contrary to popular belief, a second sequel was never intended.
Takehiro Murata: Man picking up cans. Murata has had roles in numerous Godzilla films, including the lead role in Godzilla 2000 - Millennium (1999) ("Godzilla 2000").