This herb is in the same family as mint. Their cotyledon are similar to basil cotyledon.  There are different varieties, but this particular one has purple both on top and bottom of the leaves.  The plant grows extremely fast, and like mint, you can harvest just a few leaves or cut the plant back. Their stem and branches are more like basil (while mint becomes more of a sprawling plant). As Shiso grows, it becomes bushy in one spot. In very little time, they will grow back fully for more harvests. Similar to basil, unlike mint, Shiso itself is not winter hardy. Shiso's roots do not survive the cold (40℉~32℉). At the end of the season they "bolt" and flower like basil. Their seeds are self sowing, so be careful where their seeds drop. Their seeds can stay viable even through -15℉ winters. They can spread like weed, so make sure to place them in a controlled or designated area.  The green version can be found as decoration, but in Japanese and Asian cuisine it was more of a "extra bite/dose of nutrition", but I suppose now it's seen as a culinary ornament for sushi in Japanese restaurants. 

Source: I just happen to have a ton of Shiso in my garden. Mine are not fragrant (to me), but others who have grown it have said there's a fragrance to Shiso leaves. I wonder if they can crossbreed with basils as they are so similar to basil (and since other types of basils can crossbreed).