HAPPY DAYS is a hot springs hotel in Taipei, the Xinbeitou area. In this area, people can see many historical buildings and elements which are full of Japanese heritage due to the Japanese colonialization before world war two(WWII). HAPPY DAYS hotel was also founded around 1970s by the protagonist: Fan-Ju's grandmother, Shu-Min, who has run the hotel for decades. However, "Welcome to the HAPPY DAYS," a once vibrant slogan, is nowadays the last and feeble greeting of this old hotel that still remains. Unfortunately, Grandma Shu-Min breaks her legs and is hospitalized, nobody, not even her granddaughter FanJu can run this hotel and bring it back to life. Not until a mysterious young American : Allen, who shows up at the door one day and volunteers to work at the hotel. Can a Taiwanese girl and a foreigner revive HAPPY DAYS? Can they face the challenges of running a hotel and while discovering Grandma Shu-Min's secret hidden in the hotel? With a touch of sulfur, love and friendship between Allen and FanJu will blossom and things are going to change. Welcome to the HAPPY DAYS.