Kedama no Gonjirou

One day, a timid fifth elementary student named Makoto Maegami discovers a mysterious jumping hairball stuck to its head! It then eats one of Makoto's buttons and suddenly transforms into an alien-like form named Gonjiro.

Gonjiro has the intangible ability to shapeshift itself into anything to "fit" and assist any of whatever trouble Makoto finds himself into. Thus the misadventures of Makoto entangles with Gonjiro protecting him in any "hairy" situations.

(Source: Animanga Wiki)