Bjarki Grænn (ビャルケ・グライン), mainly called by his first name in the series, is a noble Lúður Álfur that attends the same all-boys school as Sigurð, who calls him Moja (モジャ). He is very good friends with Kató and Níls, with whom they form the Celestial Bodies Research Club (天体研究部), which only purpose seems to be peeping at the girls from Rotte's school instead of anything related to astronomy.
As a minor secondary character, his role in the story was omitted in the anime and does not appear in that adaptation.
Bjarki is always seen alongside Kató. They both are also seen with Níls when the he comes back from his training. The three of them are very similar in that they are bad students who are mostly interested in watching the beautiful bodies of the girls.
In his first appearance, Bjarki and Kató trick Naoya into entering the school surreptitiously in order to act as a decoy so that they both can enter the girls school themselves, although they still get captured and beaten. After that, when they are going to their club in order to watch at the girls practicing cheerleading, they are intercepted and beaten unconscious by Sigurð who along with Dóra take their place. Some time later, Sigurð catches Bjarki and Kató with a trap using Dóra's freshly worn panties as bait and he extracts some information from them in exchange for letting them keep the panties.
After Níls returns from his training, Níls, Bjarki and Kató attempt to catch a glimpse at the bare-bottomed girl who they know is part of the "Front for the Liberation of Restraints", a legendary secret club whose members occasionally go commando and is among Rotte's group. Using Níls new wind manipulation technique, they manage to see all Lukka, Yuna and Rotte, but none of them is the person they are looking for. In a final attempt they catch a glimpse of Asuha, Míst and a cross-dressing Naoya, all of whom aren't wearing anything below their skirts. The shock of watching Naoya's loins, however, causes them to forget all that they watched.
When Rotte and her group travel to Lukka's country, Níls, Bjarki and Kató coincidentally also travel there in order to peep at the girls that should be using the Dvergur legendary hot springs. When they come across the stolen clothes of the girl, they try to get them, but the monkey that stole them quickly takes them away and makes the trio bump their heads and KOd themselves.
While Bjarki physically appears to be a bancho, he is mostly a lecherous boy who will do anything to catch a glimpse at a beautiful naked body. He appears to be incompetent in most other areas and is easily subdued by others or even by accident.