Prime Minister Fumio Kishida has appointed his son as a senior political aide, sparking speculation the 31-year-old was being groomed as an eventual successor and prompting criticism of nepotism.

Shotaro, the oldest of Kishida¡¯s three sons, was named executive secretary to the prime minister, government spokesman Hirokazu Matsuno said Tuesday, adding that the appointment was appropriate.

¡°Appointments are about putting the right person in the right role based on character and expertise, and I believe this is no different,¡± he said at the regular news briefing.

The appointment places Shotaro, already a member of Kishida¡¯s staff, within a small group that follows the prime minister almost everywhere, including meetings with world leaders, and is involved in behind-the-scenes political negotiations.

NHK said the prime minister was likely preparing his son for eventual succession by exposing him to high-level policymaking, while critics said the country¡¯s leadership is increasingly being controlled by powerful dynasties.

¡°This is, essentially, preferential treatment for family,¡± Yuichiro Tamaki, the head of the opposition Democratic Party for the People, was quoted as saying.

While placing family members in influential government positions isn¡¯t rare, even among democracies, hereditary politics is particularly entrenched in Japan. Prime Minister Kishida himself hails from a long line of Hiroshima lawmakers. His predecessor, Yoshihide Suga, is the son of a strawberry farmer and was the only leader of the ruling Liberal Democratic Party in the last two decades not to have come from a political family.

Kishida¡¯s approval ratings have already been falling due to rising living costs and distrust over the LDP¡¯s ties with the Unification Church, which has a long list of court judgments against it in Japan over its fundraising methods.

Before joining Kishida¡¯s personal office, Shotaro worked at a major trading house, according to NHK. He becomes one of eight executive secretaries, including six career bureaucrats, working for Kishida.