Masayuki Rudra Nam Ul Nasca/Chronology

Monster Capital Opening Festival Arc
Upon request by Yuuki, Masayuki's party went to the small nation Balakia that is bordering Ingrassia in order to deal with a slave trading ring suspected to cooperate with the nation its housed in. Thanks to Masayuki's The Chosen One the conspiracy was easily resolved, and the slave traders successfully taken down. However it turned out that the slave trading organization Orthrus not only enslaved humans and wild beasts, but also Elves, who upon being freed requested to return to the Great Jura Forest. Despite worries how Demon Lord Rimuru would react about the elves having been enslaved, the party decided to escort the elves back to the forest.

Upon their arrival in Tempest, after a series of events, it was decided that the party would participate in the Tournament held in Rimuru City and if one among the party won the Championship, they'd be granted the right to challenge Rimuru in battle. After easily passing the preliminaries, Masayuki's enemy was his party member Jinrai in the Quarter Finals. Jinrai just forfeited the match. In the Semi-Finals Masayuki had to face Gozul who he managed to convince to forfeit via his Unique Skill's effect as well. In the finals Masayuki faced Gobta who had obtained a Unique Skill of his own on that very day and thus was able to resist the effects of Masayuki's The Chosen One. However due to Gobta not having properly tested his new fusion ability with Ranga, Gobta ended up crashing himself into a wall and knocking himself out from the shock of what happened. Afraid that he might actually end up having to fight against Demon Lord Rimuru, Masayuki chose to forfeit the match despite being the winner, hence Gobta won the Championship instead.

Later, upon being invited to dinner by Rimuru, Masayuki reluctantly agreed. After introducing himself Rimuru revealed that he is an Otherworlder from Japan as well. After their discussion, Masayuki decides to join Rimuru as his subordinate, mainly working to promote Tempest to adventurers. Then he cooperated with Rimuru in the unveiling and public test-run of the Dungeon.

Majin Behind The Scenes Arc
When Masayuki offered suggestions toward rest-spots and save-points for the Dungeon, Masayuki's range of duties expanded to also include him as a de-facto adviser for Dungeon matters.

Eve of War Arc
Rimuru appointed him as the commander for the Volunteer Corps against his will. Since this particular corps consists of predominantly humans, it could raise unwanted discontent if a monster was appointed as its commander. Masayuki was reluctant to take the position, but nonetheless relented when Rimuru brought up the favors he owed.