Buns (or brioches) filled with custard. クリームパン。A type of kashi-pan, sweet buns or buns with sweet fillings ("kashi" means "confectionery").
The Japanese name may give rise to the expectation that this bread has been filled with whipped cream, but in fact, it is ordinary custard! This type of bread was "invented" in 1904 by the founder of Nakamuraya, Soma Aizo, on the basis of cream puffs (profiteroles). Nakamuraya was a bread shop standing in front of the Main gate (Red Gate) of Tokyo University. Later the shop moved to Shinjuku.
Comparable to buns filled with jam, and like those, available in convenience stores and supermarkets.