Shin SOS Dai Tokyo Tankentai
Genres: Adventure
Type: Movie, Episodes: 1
Aired: May 19, 2007
Studio: Sunrise
Source: Manga
Rating: PG-13 - Teens 13 or older
Synopsis:
"While packing for a move, elementary school student Ryuhei finds his father's old school notebook detailing a search for a treasure in Tokyo's vast network of underground passages. With his little brother tagging along, he and three friends from an online chat room gather and set out on a quest to find the treasure. What they discover instead is an entire underground community composed of assorted eccentrics, including a senile old soldier still performing a World War II-era mission." 

(Source: ANN)