"Futanari" is influenced by transgender porn, except the artists "idealized" them since it's fiction. Some early futanari stories involved said characters being de-facto trans or intersex women.

However, many artists nowadays started to omit the vagina part of their futanari, thus making them closer to real-life trans women, and there's also an uptick of actual trans hentai.

Other fun fact is that sometimes you can find de facto trans hentai under the otokonoko label too, current Bridget is often done like that. Allegedly done because of westerners harassed and doxxed Japanese artists that didn't keep her a femboy, because transphobes like to virtue signal about "transing the femboys" (the same exact people called me "one of those weird homosexuals that go through surgeries to convert straight men to homosexuality" for being a long-haired metalhead, also the trap meme originates from "gay bamboozling", where you tricked your mates to jerk off to trans or femboy porn).