Hikikomori Ouji no Kareinaru Yonaoshi

The seventh prince in the kingdom of Emanuele, Prince Noel, is a bit of an oddball who he has become a shut-in due to his obsessiveness in his hobbies. However, a major incident revolving around his childhood friend, Claire, the daughter of a baron, had her engagement broken off…! Infuriated by the horrible treatment towards Claire, Noel rises. Using the vast knowledge he had gained from his hobbies, he magnificently defeats the villains in his tale as a shut-in prince who's going to reform the society.