Cardfight!! Vanguard Gaiden: If  

Cardfight!! Vanguard Extra Story, カードファイト!! ヴァンガード外伝 イフ-if-, Cardfight!! Vanguard Extra Story -if-

After the conclusion of the Vanguard High School Koshien tournament, Kouji Ibuki experiences new nightmares. Nome Tatsunagi summons him to a mansion where they discover that he has the ability to see a Dark Tower called Sanctuary. This tower is altering the timeline throughout history, and in order to correct it, Kouji must first fix his own mistake from the future. Along with Suiko, Kouji travels to an alternate world and watches as Emi Sendou and Shuka summon Vanguard units to help rectify history. Unfortunately, fighting against real monsters using Cardfighting doesn't seem to be very effective in this situation.