"The variant used in the Russian language is "Аарон" (Aaron)"
Seems to me like it's not really impossible... Especially since Ayano just probably went for a name that sounded cool to her and could be decently pronounced and written in Japanese. I'm unsure if it's a frequently used name in Russia but it's there.
I will not be surprised to learn he has some connection to Yuri. He looks like a younger version of Yuri. If he is related to Yuri, that would explain why he has now twice targeted Akihito. Killing Aki surely is not part of his mission. He's there to retrieve the goods Sudou had sold him. But when he targets Aki at the start of chapter 53, he has an evil grin. Is he trying to get back at Aki for Yuri's sake?
So are we certain Aaron can't be Russian? On the other hand, if we go strictly by oldest name origin, this could be the first Jewish mafia operation in Japan (at least that I have seen in a manga).