Oui Keishou 1-i no Otoko: Harem Tengoku no Ibitsuna Ohi Erabi

Takuma Ben Maier. As his name suggests, he is a boy with a foreign father and a Japanese mother. Moreover, his father is the king of the Kingdom of Maia, with the world's 10th largest oil reserve. However, he is only the 100th in line to the throne, so he is content living an ordinary life in Japan with his mother, because he figured he would never get the chance to succeed the king. However, one day, the plane carrying his fathers and siblings crashes, killing them all. Takuma suddenly finds himself the heir to the throne, and Takuma's life changes drastically, as he tries to fend off a harem of women flocking to him for his money, including his own homeroom teacher, a TV reporter, and an idol, with only a beautiful brown-skinned ninja girl sent from his father's kingdom to protect him as bodyguard.

(Source: Momoiro Angel, translated)