Ah pretty cool! I'm Used to using MSPaint and little bit with Photoshop I do have some painted stuff but kinda hard to scan most of it being on canvas and not paper. Though I'm pretty messy with it so it doesn't exactly come out too well.
Well I assume that their design is heavily based on the yin yang motif (with the ying yang symbol even appearing on their belts) and even their personalities being kinda opposite of each other with one being more harsh and one more quiet (or so I have understood it) . And I must say I like that as well hehe
Speaking of the Ruka siblings, I got the inspiration to post the fanart I drew of them from the fact we talked about gender ambigous Nintendo antagonists (and while YW isnt Nintendo per say still close enough). And fun fact. These two aren't the only feminine looking male antagonists in Level 5 games. In fact the Professor Layton series had one too, in from of Anton Herzen (pictured below)