Itadaki Shunpei!!

The main character, Shumpei Ohki, is a high-school student and treasure hunter.　His father has ordered him to search for treasure all over the world. One day, he travels to Kalimantan to obtain a mysterious ruby ball, but comes into conflict with another group of treasure hunters. The latter collect "treasure balls" from all over the world, and call themselves the "Dark Star Gang". Shumpei is lucky enough to obtain the ruby and returns to Japan, but Paucha, who was guarding the ruby, follows Shumpei to the Oki family...

(Source: Kadokawa, translated)