expression, godan verb (-tsu)
to take revenge in an unexpected place or context; to hit someone where they least expect it
Proverbial expression meaning to retaliate or get even in a completely different setting from where the original offense occurred. Often used figuratively for settling scores in unrelated situations. The literal image is attacking an Edo enemy far away in Nagasaki.
He defeated his old rival in a completely different industry, truly taking revenge in an unexpected place.
あの会社は、かつての取引先に裏切られたが、今度は海外市場で成功して江戸の敵を長崎で討った。
That company was betrayed by a former business partner, but now they've succeeded in the overseas market, getting their revenge in a different arena.