I found this little guy growing in a crack in some cement steps outside someone’s home in my neighbourhood. It looks like shiso しそ (紫蘇, perillia) to me. The edible plant apparently looks similar to stinging nettle, but since there was some potted shiso growing nearby, I figured that it had probably reseeded itself naturally. Also, I touched the plant quite a bit to inspect it and experience no stinging.
To me, shiso is a distinctly Japanese flavour. It comes in green and purple varieties, and can be seen growing in many potted gardens in Tokyo, as well as in supermarkets. It is typically served with sashimi or cut up and mixed with rice, and the purple variety is mixed with ume boshi (pickled plum) and then mixed with rice to become onigiri (rice ball). A couple years back Pepsi came out with shiso flavoured pepsi and though it did have a distinct shiso-flavour, which I love, was pretty undrinkable, as most novelty sodas are. A friend of mine once got creative and made shiso mohitos, which I highly recommend trying.