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.
1/2 cup mayonnaise, preferably Japanese
2 tablespoons Sriracha hot sauce, plus more to taste
1 teaspoon freshly squeezed lime juice (optional)
In a small bowl, mix together mayonnaise, Sriracha, and lime juice. Taste and add more Sriracha to desired spiciness. Serve immediately or transfer to an airtight container and store in refrigerator for up to a month.