Some Japanese women marry late in life, if they marry at all. One reason for delaying the trip to the altar is a reluctance to venture out from their comfortable nest to share life with someone else. Hotaru Amemiya (Haruka Ayase), the heroine of this romantic comedy, must decide whether to take the plunge into marriage after her roommate and boss Takano (Naohito Fujiki) pops the big question.

The drama picks up three years after where the first 2007 storyline left off. Back then, Hotaru put on the façade of being an active working woman by day, but turned into the ultimate homebody at night who lounged around in sweat pants drinking beer, eating dried fish and gazing at the fireflies in her garden. Hotaru's life got complicated when she allowed some men into her life. She eventually ended up with Takano, although she regarded him somewhat like a big brother.

Is Hotaru ready to take up the challenge and answer Takano's proposal? The drama captures the tentative feelings of many young Japanese women.

职场上是一个美丽大方能干的白领丽人，但回到家是一个没有女人气氛，穿着邋遢的运动服，扎着发髻，躺在榻榻米边喝着啤酒边看漫画…。2007年一部描写「与其谈恋爱，不如在家睡觉」的「鱼干女」的新形女性形象引起巨大反响的《萤之光》。

三年后，「鱼干女」复返了！！

雨宫萤（绫瀬遥饰）从赴任的香港工作结束回国，与高野部长（藤木直人饰 ）重逢。尽管三年间通信全无，也像以前一样住进了高野的家。看到懒洋洋的鱼干女姿态的小萤，高野部长不禁哑然。小萤的鱼干女力量已着实上升！

这样的小萤被高野部长的一句「结婚」，开始思考「结婚是什么？」。连「恋爱」也没有自信的小萤，对突然降临的「结婚」 二字，究竟鱼干女小萤成长为怎样的女性呢…。