Grinsha is another White Overlord Inves and is responsible for countless murders of the old civilization trapped in the Helheim Forest, and has targeted Japan next.
He is summoned by Rosyuo to assist Redyue. Under Redyue's leadership, he is ordered to capture a civilian for a sacrifice. Apparently he found where Kouta's sister, Akira Kazuraba and the survivors are hiding. He was about to be destroyed by Gaim Kiwami Arms and Baron Lemon, he is saved by Redyue and knocked unconscious until he woke up for another round with a Rider later.
Grinsha is shown to be way more powerful than Demushu and Dyudyuonshu, as he is equally matched with Gaim Kiwami Arms.