The Invincible Cosmos
season 1 episode 36
Dr. Umon calls Daisuke and Koji to show them the way that Grendizer and Double Spazer can unite together and fly. The objective of this is to minimize the need for Grendizer to have to lock in and out of Spazer as these are Grendizer's weakest moments and he is helpless in them.
Where to watch:
Shahid VIPTV Tokyo