幼馴染の菜々子の声援を受け、ラグビーの試合で張り切るワタル。だが、菜々子とハヤトの親密な様子に、胸が騒ぐ。そのとき、突如現れた宇宙化猫ムーと、ダークサンダーエナジーを浴びて出現したレッドキングにより街は大混乱に！ エックスが立ち向かったとき、ムーがエックスに甘えるようにじゃれついていった！ ムーの目的は？ そしてワタルの恋の行方は……？
Encouraged by her childhood friend Nanako, Wataru played passionately in a rugby match. However, he grew uneasy seeing Nanako and Hayato becoming closer. At that moment, an space cat named Mu suddenly appeared, and the city was thrown into chaos by the appearance of Red King, powered by Dark Thunder Energy! As Ultraman X faced off against them, Mu playfully approached X, as if seeking affection! What was Mu’s true goal? And what would happen with Wataru's love life...?
