The Mysterious Underground Men

The Mysterious Underground Men summary: Chiteikoku no Kaijin is a sci-fi manga that follows boy-scientist John and his crew as they battle against the underground civilization's plan to seize control of the planet. After losing his father in an airplane crash, John invents a reliable, high-speed train that can travel through the Earth. In pursuit of his father's final wishes, John partners with Mimio, an intelligent rabbit, to embark on a journey to the Earth's core aboard the new rocket train. Upon arriving, they encounter an underground society governed by a queen who has her sights set on dominating the planet. With the help of his team, including Uncle Bill, John miraculously escapes to the surface. Upon returning to the underworld, he constructs a new rocket train to continue the fight.