I was out of stamina so clicked few times on "home" button to watch some pictures. After few clicks i heard something like "ehe". There was Nazuna figurine on bookshelf. Guess its not a secret - but noticed it first time. After few more "home" clicks another "ehe" - screen with city - Nazuna in window in down-left corner.More clicks : very small white figurine of Nazuna in door of mountain castle. And last two - training grounds - Nazuna behind a wall and shop - Nazuna on ground behind barrel. Its fun to find such little secret after playing it for so long . Well too bad there isn't any reward for it (like 6 star Nazuna for example ).
English is not my language - sorry for mistakes ;p