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.