Sen is one of Kutal's twin nephews, consistently appearing alongside his brother Rei and sister Este, emphasizing their inseparable bond since life began until its end. He wears a blue shirt, distinguishing him from Rei's green. Introduced carried by a large Pterodactyl, Sen and his siblings were rescued by Kutal, Mushra, and Sago, after which they sought to stay with their uncle. When deemed unsafe, Sen participated in a "Test of Courage" through a jungle graveyard, across a river log, and up a hill to prove bravery.

Having succeeded, Sen traveled with Kutal, Mushra, Sago, and Yakumo. At an abandoned school, Sen and Rei wandered off, discovering a triceratops inside. Danger prompted them to flee; they returned after the building's demolition, witnessing Kutal and Sago's Hyper Forms. Sen often stayed near Hakuba during Enterran battles. In the final arc, he observed the fight against Lanancuras from afar. Post-conflict, Sen helped rebuild the world with other Enterrans and humans.

Concluding, Sen joined Kutal, Sago, Binka, and his siblings in deciding to travel westward per Yakumo's guidance, collectively resolving to search for Mushra as part of the group.