Brilliant Blue (2004)

Blurb:
When Shouzo Mita left home, he thought it would be for good. Although he followed his father’s career path as a construction manager, Shouzo never wanted to enter the family business—that is, until dad got laid-up with an injury. Forced to return home and oversee his father’s company, Shouzo finds that a lot of things haven’t changed, but some things have. Nanami, a childhood acquaintance, has gone from being an awkward fatty to a sparkling pretty-boy straight out of a shojo manga. As an electrician contracted to work for Mita, Nanami’s simple, naive charm and healthy appetite manage to flip Shouzo’s switch. With the choice between remaining independent and accepting responsibility for his family even more complicated, what will Shouzo do?

Source: www.anisearch.com/manga/3464