Maru is a meal made easy: at lunch the restaurant does good grilled fish teishoku (set meals), among other things; in the evenings, courses with sashimi, seasonal sides, a main of meat or fish and a choice of Japanese-style desserts. If you want something lighter, you can also order small dishes (like grilled mushrooms or honeyed walnuts) designed to go with sake.
There is table and counter seating, a classy vibe but no stuffiness. Walk-ins are welcome and staff speak English. It's in the Shibuya Stream complex, with direct subway access.