Orsted/Chronology

Volume 2 - Juvenile Period - Home Teacher Chapter
He appears for the first time in the Red Dragon mountain range, killing two Red Dragons in self-defense with one strike each. Noticing the abnormal mana gathering in the Fedoa Region as a result of the Metastasis Event, he curiously heads in its direction.

Volume 6 - Juvenile Period - Homecoming Chapter
Initially, he and Nanahoshi were walking by the Red Dragon Lower Jaw and meet <>. After hearing that Hitogami visits Rudeus in his dreams, he fights against <> and easily defeats Ruijerd and Eris while holding back, and almost kills Rudeus after rupturing his inner organs. However, he was scratched by Rudeus' Rock Bullet after being caught off guard. He then spared and healed Rudeus per Nanahoshi`s request.

Volume 15 - Young Man Period - Human God Chapter
Under the orders of the Human God, Orsted was ambushed by Rudeus who managed to damage him with magic powerful enough to utterly decimate the city-sized location of the battle, forcing the Dragon God to fight seriously. Summoning the "Godsword", he completely overwhelmed Rudeus by destroying the Magic Armor and slicing off his right arm, but then he faced Eris who managed to put up a fight against him due to her arduous training. Hearing the story about Hitogami's threat from Rudeus, he decided to make him his comrade in his fight against the Human God.

Volume 16 - Young Man Period - Kingdom Chapter
Rudeus learn more about Orsted, his history and his curses. He also explained to Rudeus about Laplace and flow of destiny before moving over to their plans to defeat Hitogami. They decide on their first goal to make Ariel the queen of Asura Kingdom, correcting the course of history which Human God disrupted to gain an advantage over Orsted.

Volume 17 - Young Man Period - Asura Kingdom Chapter
He ordered Rudeus to help princess Ariel and kill Hitogami's apostles who changed the flow of fate. He tailed Rudeus and his party from the shadows, occasionally appearing to advice and help. In the venue, he answers Rudeus' emergency call for help and easily kills Water God Reida. After the events in Asura Kingdom, he told Rudeus the real truth: Orsted is a looped existence that has experienced the world for more than 100 times and that Rudeus is a new existence outside the loops.

Mushoku Tensei Sequel
By the time of Mushoku Tensei's end, Orsted's mission to kill Hitogami is one of the major story threats that remained unresolved. However, Rudeus did see a vision where his and Roxy's daughter, Lara Greyrat, helped Orsted and an unknown individual, presumably Shinohara Akito, enter the void between worlds to finally kill the malicious god. Thus, Ornsted is likely to remain a major character in the planned sequel series.