在遭受「幻影帝國」進攻的地球裡,光之美少女是世人共知的存在,人們不時從新聞了解各小隊為了自己的所屬國家戰鬥。成為最惡獸攻擊目標的「藍天王國」公主白雪姬,在一次侵略中逃亡到日本的光之丘地區,過程中遇見了地球的守護神「蔚藍」。蔚藍賜予她成為光之美少女的使命,不過孤僻的小姬對於這份使命極為恐懼,在一次次的戰鬥中選擇逃避。
蔚藍於是再給予小姬一份稱之為「愛的結晶」的力量,讓她能夠尋找命運中的同伴。怕生的公主衷心想交到朋友,卻不知道如何運用結晶,結果只想著「這個砸到的人就是我的朋友!」就把它丟了出去。就這樣,竟然砸中了人生中第一個朋友與夥伴-愛乃惠。
Nine universes of the previous Kamen Riders from the Heisei era are merging into one, something that would destroy all the worlds. To prevent this, Tsukasa Kadoya transforms into Kamen Rider Decade and is told that to protect his own world he must travel to all of the other Kamen Riders' worlds (Another Rider's worlds) and eliminate the anomalies in those worlds. Along the way, confronting the mysterious Narutaki and the thief Daiki Kaito, they are joined by Yusuke Onodera of the World of Kuuga and Kivala of the World of Kiva.