Ah, good, the doll was capable of speaking. At least there was that, then. The bird likely couldn't, but beggars could hardly be choosers.
"Please, come inside. Standing outside like this is hardly the place to talk about such matters." Ruler remarked in reply to the Rider and doll, turning slightly in a motion that was a touch more ostentatious than it would have been in different attire, before setting off to reenter the church, gesturing for the pair to follow.
Rider's question seemed to spark a bit of amusement from the Servant, Ruler nodding to himself a bit before replying. "A fair question, if the Holy Grail has not provided you with that information. You may call me Ruler. I am the administrative-class Servant summoned by the Holy Grail itself, a Heroic Spirit without a wish who has been selected to serve as an impartial moderator to this war. I was told that, ordinarily, a representative from the Holy Church would be present as an overseer, but in this particular instance he and I spoke shortly after I was summoned, and decided that it was for the best if that role was shouldered by me alone. He was no combatant, and when presiding over a battle between Servants, it is imperative that one has the power to protect oneself."
"As Ruler, I am simply here to protect the foundation of the Holy Grail War. This one is of an unusual make, you see, which I believe is at the root of why the Holy Grail deemed that a Ruler was necessary. Your Master mentioned the idea of fighting 'six other participants', but in this war there will be far more than that. For some reason or another, the Holy Grail has amassed enough magical energy that the standard limitation of seven Servants no longer exists...in fact, currently, more than seven have already been summoned. In such a case, this war will no doubt be a chaotic one, and there may be those who seek to undermine the Grail War, wreak havoc upon the city, or something of that make. I am here to prevent that."
At the doll's question, though, the Servant paused for a moment before voicing his reply. "Well, as I said, I am meant to be impartial, so while I personally would like to impose a decent set of rules, the ones I will be enforcing are rather bare-bones. First and foremost is simply the necessity of the war's secrecy. While mistakes do occur, excessive carelessness or, worse, conscious efforts that undermine that secrecy and risk exposing it to the general public will be punished. If you were to instigate combat in a crowded area of the city at midday without taking any precautions, for instance, then I would have to step in. Next would be the importance of this church as neutral ground. No combat is to occur here. Similarly, if a Master were to lose their Servant and fears for their life, then they would simply need to come to this church and I will take efforts to protect them until such a time that they can arrange to leave the city."
"Besides those, there's the matter of the city and its population. Many Servants will have Noble Phantasms that affect large areas, or have abilities that rely on harvesting magical energy from others. As a result, there are no explicit rules placed upon property damage or nonviolence towards nonparticipants in the war, so as to not unfairly disadvantage those parties. However, as with the war's secrecy, carelessness will not be tolerated; if you destroy a large portion of the city or slaughter innocents when other options were available to you, punishments will be handed down. I must also warn you that there is the prospect that the Second Owners of this city may charge you for property damage following the war, should you and them both somehow survive. Similarly, while I will begrudgingly allow the killing or manipulation of nonparticipants for such things as replenishing a Servant's prana, moderation is key. Do not attempt to cut a path of slaughter through this city, as otherwise I will not stand by idly."
"I believe that covers the essentials. So long as you keep that much in mind and exercise common sense, you will have nothing to fear from me. If you require any additional clarifications though, then by all means."