I never tried to look, so I don't know if anyone else ever mentioned this, but ASL's "Brotherhood cups" (兄弟盃) is reminiscent of the "Peach Garden Oath" from the Romance of the Three Kingdoms novel (the fiction, not the actual history).
The vibes of it is even stronger in the side story sensei made, where there's a scene of the ASL trio having the sake as grown ups under some kind of flowering trees. From what I can see those trees are sakura, but peach blossoms and sakura look very similar.
(you can read the side story here BTW)
In the Three Kingdoms, three men gathered in a garden of peach trees, offered some offerings, and then made this oath of brotherhood:
When saying the names Liu Bei, Guan Yu and Zhang Fei, although the surnames are different, yet we have come together as brothers. From this day forward, we shall join forces for a common purpose: to save the troubled and to aid the endangered. We shall avenge the nation above, and pacify the citizenry below. We seek not to be born on the same day, in the same month and in the same year. We merely hope to die on the same day, in the same month and in the same year. May the Gods of Heaven and Earth attest to what is in our hearts. If we should ever do anything to betray our friendship, may heaven and the people of the earth both strike us dead.
Kyoudai Sakazuki in general is something that the yakuza do, but the feeling of brotherhood oath that ASL swore is more similar to the Three Kingdoms one, especially because there's literally 3 of them.
In the actual text of the Three Kingdoms novel, there's no mention of wine being drunk while the oath was made, but it's a pretty common depiction in adaptations that they do drink some kind of wine (see the pictures above).
I think this is just a one time reference too, and not anything theory-worthy, but who knows.