I may not be much of a sushi eater, but I certainly know the pinkish spicy sauce that adorns many rolls because it's my all-time favorite condiment—sriracha mayo!
You can go with more traditional Japanese hot sauces, but most times this sauce is born from the combination of sriracha and mayonnaise, so to create a good facsimile, that's as far as you really need to go. However, I do recommend the use of Japanese mayo, which is slightly sweeter and a little thinner than supermarket staples like Hellmann's, although if not eaten side-by-side, it can be tough to pinpoint the slight difference in flavor.
A splash of lime juice livens up the sauce, but it's also not completely necessary when the sriracha does most of the work of adding a spicy and garlic-y depth to tangy and creamy mayo. It makes what I consider a supersauce, which goes beyond sushi and is incredible on burgers, fries, sandwiches... this list could go on for a long time.
About the author: Joshua Bousel brings you new, tasty condiment each Wednesday and a recipe for weekend grilling every Friday. He also writes about grilling and barbecue on his blog The Meatwave whenever he can be pulled away from his grill.