Inga, a mysterious boy who follows Shinjūrō. It seems that he and Shinjūrō are tied together by a curious bond, but no one knows the nature of it. Inga is usually protected by Shinjūrō, but when a crisis is at hand, the roles are reversed. When the time comes, Inga can turn into a mature woman and help Shinjuro solve cases.

From the anime UN GO.
Hope you all like it! Just finished watching this anime a while ago, its pretty good in my opinion, if your into mystery, then this might be good for you. 

More details in: un-go.wikia.com/wiki/Inga