Here's some things..
1. Every time Shinichi is brought up to Vodka(like twice, since ep1) he remembers Gin giving Shinichi the poison.. during this flashback it usually shows the part when as Gin is about to do it Vodka seems reluctant and says "Aniki(bro..)"
2. Episode 500: After Camel crashes the van.. and Rena comes out to face Gin, Vermouth, etc.. Vodka says something to the effect of "I guess the mission is a success.. Shouldn't we go?" and Gin reacts to Vodka saying this, looking I almost wanna say suspicious of Vodka then saying "ok"..
If any of you can think of anything pecuilar, let us know.. i'll edit when I think of more























