I believe the irony may be that Shinzo Abe and his LDP party have pushed ultranationalist policies, and he himself has been vocally anti-Korean multiple times, eg his demand that South Korea have 'confort women' statues removed worldwide as part of a comfort women reparations deal being discussed with SK (they were rightfully pissed). Except in his support for the cultish Unification Church (the 'Moonies'), whom are South Korean founded and well known for excessive financial exploitation of their members, not unlike the Scientologists. He was then killed by an assassin who held him culpable for the Moonies taking advantage of his mother to drain her life savings in church donations to secure her afterlife.

So, ultranationalist-party anti-Korean PM assassinated because of his support of a Korean cult-church. Ironic, poetic.

P.S. take his 'anti-Korea stance' with a grain of salt though as I can't provide very good sources because what I've read is (poorly) translated summary links to news articles in Korean, and I don't know Korean. But the general vibe is they did not like him one bit.

Abe's assassin was a alt right incel who turned down that path because his mother gave all the family's money, including his college savings, to a cult. At a certain point, he realized that the right wing leaders he turned to were in cahoots with the cult, and he directed his anger to them.

I don't know much either, but it was unexpectedly funny when I heard a Japanese grandma I know say "Arigatou, Shooter-san. Wish you would've done it sooner though."

i think it refers to Abe being shot by a homemade gun. doohickey can refer to crude, handmade devices