If mezcal is tequila's cousin, then soju is sake's tough uncle. Like sake, soju is made primarily from rice, but it's distilled, putting its alcohol content, and taste, somewhere between sake and vodka. Soju also differs from sake in that it comes from Korea, not Japan, though a similar beverage with a similar name - shochu - is popular in Japan as well. You'll find soju at liquor stores with large selections, Asian markets that carry alcohol, such as Reliable Market (45 Union Square, Somerville, 617.623.9620), and Korean and Japanese restaurants, including Shabu-Ya ( 57 JFK Street, Cambridge, 617.864.6868), Korean Garden (122 Harvard Avenue, Allston, 617.562.8989), and Koreana (154-158 Prospect Street, Cambridge, 617.576.8661). The last serves soju cocktails - the Green Boston and Purple Denver, for example - named for the colors of their ingredients and major American cities. Soju can be served straight up, flavored, mixed with juice or soda, or plunked into beer for, you guessed it, a soju bomb. That's one bomb Korea is welcome to share with the world.