Think the original Ultraman, but with cheesier special effects and a James Bond/Man from U.N.C.L.E. type plot with secret agents who are part of a secret organization called Unicorn. The lead bad guy is an alien overlord named Emperor Guillotine who has a terror group named Gargoyle Gang do his bidding and try and take over the world. They initially built a giant robot to try and do so, but the main character, a boy named Johnny(Daisaku in the Japanese version) takes control of it by being the first to speak into its voice control, which is stored in a watch. Throughout the series he and Unicorn fight off Gargoyle's giant monsters and assassins.
The whole series is super fun to watch if you like this sort of stuff. Vid related is from an episode of the show.https://www.youtube.com/watch?v=yayZr8fQJPY
I figured it would crossover well with Hilda because both series feature a young kid going on adventures and encountering monsters and stuff.