I read the beginning of this manga some years ago but forgot its name.
There is a scene in which the main protagonist, who is a teenage boy and the head of a ninja clan is tested by an old grandma before other ninjas : he must pass through a small hole on a wooden wall and he succeeds in doing this by instantaneously putting his shoulders out of joint and making the width of his body smaller.
Does anyone know the name of this manga?
Thanks.