Redrappy, I think we need to step back and figure out what you are arguing. Shibuya no doubt inspired both, though as Tim points out the area has inspired a LOT of media. Anime, manga, other games - Shibuya itself is featured or inspired by. From where I stand, that's about as strong a connection as New York City and just about any media property based there - alleyways, sewers, pizza, taxis, brooklyn accents. Still, I wouldn't say Home Alone 2, Spider-Man, TMNT, and Ghostbusters are joined at the hip - they just feature a similar location.
So in that regard, yeah I can look at those screens and think "hip metropolitan Japan", but beyond that I think both properties are very much their own thing. I mentioned vinyl figures because that is where Splatoon feels most associated with visually. Kids with squid features and with an almost plastic quality to them. Looks like some trendy thing you'd see for sale next to Mighty Muggs or stuff like this:
http://www.squidkidsink.com/ That's not a knock on them, I just think they are very much a product of whats hip in Japan now and its very much in line with the crazy sort of toys and anime happening right now - like Panty Stocking.
JSR, meanwhile, is much more a product of the late 90s, pulling from Ryuta Ueda's gritty sketchy art style and inspired by the youth culture of the late 90s (not 2015 as Splatoon feels). Not to mention we have the war on gangs and pirate radio aspects which feel straight out of the 80s and 90s war on graffiti and gangs.
Both are based on Japanese youth culture (with a 15 year seperation, however) and an area of Japan, but thats about the extent for me. Outside of that you have plasticine 3D squid kids that look like vinyl toys made in 2015 compared to flat rough sketchy street gangs fighting cops that look like something out of a late 90s sketchbook.