My son is a what?! (Kamen rider Geats X nijisanji X multi crossover)

Nina Kosaka, NijisanjiEN Third wave Ethyria, was Excited when she learn that her adopted son was coming back home after studying aboard for so long.

But one day when she and her friends were hanging out, there were trapped in some sort of force field with weird monster coming out of nowhere killing everybody.

Just as they were cornered and about to be kill, they were rescued by... her son?!

What has her son been doing aborad?!

Follow Shiro Kosaka, son of Nina Kosaka as he fight to save the world, as Kamen rider Geats