Danbo is a character from a manga* called Yotsuba&!, which chronicles the amusing life and adventures of the 5 year old girl the series is named after. Yotsuba&! was first published in August 2003 in Japan.
In issue 28 (from April 2006) one of Yotsuba’s older friends, a girl named Miura Hayasaka, dresses in a robot costume made from cardboard boxes as part of a school project.
Yotsuba discovers her dressed in the costume, so Miura playfully convinces Yotsuba that she is an actual “attack robot”, powered by money inserted into the slot on the chest. Miura names her “robot” Danbo, although around the Internet she can be known by several variations.