in Estria there were  different continents for different races, Elvina for the Elves , Humas for Humans, Beastlain for the Beast people Dwargon for the Dwarves E.t.c. In this continents there were further different countries, and in this countries there are Adventurers and Explorers. Aventurers usually kill monsters and clear dungeons while Explorers explore ruins and other suspicious locations while searching for treasure like any typical Explorer would. That was why this Explorers wanted to explore the castle as it was basically their line of work. 

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  He looked up and saw a shadow in front of him the shadow gradually took form to reveal a stunning onee-san donning a full secretary like outfit glasses and everything. she said in a gentle voice"what are doing here human"in that gentle voice he sensed an enormous amount of power, power that could swat him away like air. Now we must know that he is an A-Rank Explorer only lower than a S-Rank. He alone could wipe out an Entire Army but in front of this woman he felt powerless. He knew he was no match for her so he just gave up. seeing this she smirked and said "alright human i will forgive you for trying to interrupt my lords rest on one condition". He asked what the condition was, she smiled "become a priest of my lord and stop all this pesky humans from disturbing his peace". He was curious about the person who she kept callin her lord so he asked. She looked at him intensely the moment he asked the question, she started releasing aura around her body , he felt like his soul was about to leave his body then she suddenly retracted her aura he laid flat on the floor while gasping for air he was just thinking this lady is scary is she trying to kill me?. She asked him if he will accept to be the priest and he immediately accepted.  Then she asked if he knew about Rixton and he said yes. Well everyone knew who Rixton the Guardian of the Human Race was. She said he was in the castle of Rixton who was her lord and well Rixton didn't like disturbances when he was sleeping that was why whenever someone came to the castle she had to kill them to stop Rixton from obliterating the Human Race, upon hearing this his ears nearly bled he couldn't believe this was the castle of Rixton. Rixton was the Guardian of the Human Race, he first appeared when the human Race was under attack from the Demon Race, then the Guardian of the Demons was a little ambitious and he wanted to clean up humans as they didn't have Guardians while the other Races had their Guardians. That was when Rixton first appeared and he taught them how to use magic and protect themselves and he gave them a Hero who succesfully defeated the Demon King. That was when his Legend started. T.B.C