In astrology, The Planet Saturn's mythology suggests that it represents birth, sex and death. There isn't much place for sex or birth, for that matter, in this series and the aspect of death is most focused on in Nashiran's character. His martial-art style of Hapkido was picked for SaturnAstro because it combines the use of pressure-points in with other assortment of highly precise movements. Pressure-points can be considered the more deadly techniques to martial arts because of the fact that you can kill with them. However, such moves take years of dedicated practice really be good at such a skill which still would not be drawn out of an honorable combatant unless they are stopping themselves from being killed.
Saturn can be a depressing planet because it is so limited, worldly and aggressive because they can either be so powerful and so great they are apart from society or are constantly frustrated with failure. So thus, Nashiran can be very realistic and optimism can be difficult for him to express in situations where it is needed most.
This character as defined in Astroranger is of the sort that they are so dedicated the cause he is fighting for that he would be willing sacrifice himself to and end if he believes it necessary.