Upon attending the opening ceremony of a museum in April in Tottori Prefecture, veteran Liberal Democratic Party lawmaker Shigeru Ishiba made a sidesplitting appearance by dressing up as Majin Boo — the pudgy, baby-like villain in the popular anime “Dragon Ball.”

Funny as it was, his imitation of Majin Boo, the ultimate antagonist in the show, was apt in one sense: Ishiba is now on course to become one of Prime Minister Shinzo Abe’s biggest adversaries in the LDP’s presidential election slated to kick off in September.

Famous for his extensive military knowledge, which has earned him the title gunji otaku (military geek), Ishiba, 61, has held multiple portfolios from agriculture to defense.

Under the Abe administration since 2012, Ishiba supported the prime minister first as LDP secretary-general and then state minister in charge of regional revitalization. In summer 2016, however, he decided to break free from Abe’s control by reportedly rejecting his request to stay in the Cabinet.

That was the beginning of Ishiba’s battle against Abe that has made him an intraparty critic today. Ishiba now frequently makes headlines by criticizing Abe over controversial topics.

Although he hasn’t officially announced his intention to run in the September race, Ishiba is widely expected to throw his hat into the ring in what would amount to a “revenge match” against Abe, to whom he had narrowly lost in the 2012 presidential election.

“It’s unconvincing, any way you slice it,” Ishiba blogged in late March as he took a swipe at Abe’s stated bid at the LDP’s annual convention to amend Article 9 of the postwar Constitution by adding an “explicit reference” to the Self-Defense Forces.

Ishiba has spent the past year questioning Abe’s proposal, which he said ignores a more drastic overhaul of war-renouncing Article 9 that was officially adopted as LDP policy in 2012.

Both the LDP’s 2012 constitutional revision plan and Ishiba’s own proposal amending Article 9, unveiled in February, involved deleting the phrases about Japan’s disavowal of “war potential” and the “right to belligerence.”

In the blog post, the right-leaning politician made no secret of his dissatisfaction with Abe, who he said “offered no explanation (at the convention) as to how to boost our nation’s deterrence abilities amid the rapidly changing security environment.”

In January 2017, Ishiba openly questioned the government’s reported decision to approve Emperor Akihito’s 2019 abdication, which will be the first live relinquishment of the throne in more than 200 years, as a one-off exception, claiming future emperors should also be allowed to retire if they wish to, instead of being destined to reign until death.

Despite his vociferous criticism of Abe, Ishiba, in reality, is fighting an uphill battle, disadvantaged by his relatively weak clout in the LDP.

Although Ishiba has his own faction, it remains the second-smallest, with his backers one head short of the minimum 20-member endorsement needed to register as a candidate for the race.

Aside from being a military buff, Ishiba is known for other geeky pastimes: the Tottori native is a self-professed train-spotter and fan of pop idols from the 1970s, especially the now-disbanded female trio Candies.