Shin SOS Dai Tokyo Tankentai

Synopsis

While getting ready to move, elementary schooler Ryuhei discovers his father's old school notebook, which outlines a treasure hunt hidden in Tokyo's labyrinthine underground tunnels. Together with his younger sibling and three online friends he has recently met, Ryuhei embarks on an exciting adventure to find this hidden fortune. Along the way, their exploration uncovers an entire subterranean society populated by strange individuals, including a senile former soldier still carrying out a World War II mission.