Izakayas with great selections of both sake and craft beer aren't all that common in Tokyo, so Bakushuan is worth knowing about for that reason alone. But even without drinks, the excellent food stands on its own merits. It's a more delicate, refined version of simple izakaya fare that's designed to complement both sake and craft beer. Sashimi, grilled fish and tempura are all first rate, and they're supplemented by a nice assortment of sake-friendly small dishes.
The management is quite serious about promoting craft beers, so you're more or less required to start off with something from their tap list. There are around a dozen domestic brews, including fine choices like Shiga Kogen House IPA and Iwate Kura Oyster Stout. Check the Japanese menu for details or ask your server. The staff are also very helpful with sake recommendations (although knowing a bit of sake terminology in Japanese will make this process smoother).
As with many seafood-specialty izakayas, the day's sashimi platter is an excellent place to start. Ours featured some surprisingly tender minke whale and excellent Spanish mackerel. The seasonal vegetable tempura was light and delicate, and not a bit oily-tasting. If you're using the English menu, be sure to ask about the daily specials (or take a peek at the Japanese menu) for dishes featuring seasonal vegetables and the catch of the day.
If you decide to explore the sake list, the platter of smoked camembert, smoked quail eggs and smoked ume plums makes a delightful accompaniment, as do the crunchy Akita-style smoked iburigakko pickles with cream cheese. Bakushuan's creative interpretation of potato salad is also worth a try.
The dining room is fairly compact, although tables are adequately separated. The decor is tasteful and restrained, and the atmosphere is relaxed. Budget around Y4000-5500 for dinner with drinks; they're also open at lunchtime with a far simpler teishoku menu starting at Y950. Dinnertime reservations are highly recommended. Bakushuan also has branches in Otsuka and Ebisu.