Summoned in the state at the start of his reign as the perhaps most successful Persian ruler if we go by the years of rule, just after his first succeeded goal: the revenge on the Arabian raiders. In this Class he displays a more rather hotblooded demeanor. In contrast to other Classes where he is summoned as more experienced Shah and commander he manifests in this Class as youthful warrior that lead the campaign against the Arabs.
He is initially a quite stern and direct person who is rather mistrusting and slow to be approachable as he was lectured by his mother to be wary and cautious for many noblemen and palace officials are perhaps trying to use him as pawn in their plays. He has this advice rather fresh in his memories and lacks the experienced human knowledge and judgement of his older years. Although he has access to the memories of his later years they are rather distant visions.
He has experienced in his youth some of the assaults of these raiders of the southern deserts, and he swore as his mother was in tears of fear to ensure that she have no more to see such atrocities. So he was determined to end the terror that his people had to endure and execute an example on the Arabs.
Hence he slaughtered the Arabs. If warrior or not, if civilian or not, didn't matter. The fact that they were Arabs was enough to let them be enemies that he must defeat. They saw in him a merciless devil, a Djinn in human shape. He and his plundering cavalries made such a terrifying impression that many tribes amongst them even the biggest Arabian tribe the Banu Tamim fled and didn't dare to approach the land. They chose freely the hostile desert than to return in their old settlements in fear that he may return and repeat the assaults.
He displays this trait through a rather serious and cold demeanor. However in his homeland he was celebrated as hero who ended the horror and passed his test as ruler as Shahansha (King of Kings of Eran and Aneran) of Persia.
However he is more warm hearted and compassionate than it seems as he was just able to do these deeds through his love for his family and his country. The tears of Ifra, his mother broke his heart and he swore that he can't allow that she endure this again, nor did he want that his siblings have to endure this pain. So he is rather more easy going in the environment where he almost behaves more like a protective older brother then a cold man. So he can't tolerate any harm on children. Also although he fights ruthlessly and rather mercilessly he has a feeling of honor and respect so he fights his opponent fair and doesn't draw upon underhanded methods, as long as his opponent behaves this way, he refrains from using these methods but should his opponent employ underhanded methods or other means of combat than open and honorable battle he will see no problem in using self underhanded methods according to the situation.
Demeanor as Servant:
He is at first a rather dutiful Servant who prefers to start the fighting with the other Servants as fast as possible. However he has still some traces of the wise commander he will later be as he rather reluctantly acts more mindful and cautious until he has information About the other Servants. However he still is curious about the world and how other cultures are, like as he once tried to incognito discover the Roman culture. So he likes to taste their dishes and at least give their festivities a try. However he still holds his own culture in high regard as through the experiences in his youth he has found a very affectionate sight on his homecountry.
He holds out of this reasons the Servants of the old Persian world in high regard as he wanted to rebuild the former Persian glory with the Sassanid Empire to reestablish the old state during the Acheamenid Empire which is the reason why if he encounter the old Persian rulers he is highly excited and would almost rather have with them a talk over some mint tea than to fight them if possible. Especially Kyros the Great is for him a symbol of glory, the divine founder of the Persian Empire. Also to the Arsacid rulers, the dynasty before the Sassanid rule has his respect but no true acknowledgment beyond the respect he pays them for freeing Persia from the Greek rule. Despite that he greatly dislikes the Macedonian Empire what he sees as the predecessors of the Roman Empire he still respects for how they treated the Persian country with respect and had consideration for their religion and spirituality. Though if he encounters a Servant of them he is incited to demonstrate the superiority of Persia.
Towards Arabian Servants he has still great contempt and resentment, especially as he has through the Grail acquired the knowledge of the Sassanid Empire after him and that they caused the downfall. So he is quite hostile against them and should he encounter a Muslim Servant he will immediately assault them with the ferocity of a Berserker Servant to exercise revenge for his country as he sees the today Iran as conquered by Arabs and not truly Persian anymore. In this case he is regardless if he has personal disdain for another Servant will help them just to utterly defeat and humiliate the Arabian Servant. This was also the reason why he couldn't ally himself with the short-lived Palmyrene Empire. His opinion towards other cultured Servants is rather curious and without any specific prejudices.
Aside that he is serious during fights, is he still rather conscious to keep bystander out as much as possible, as he dislikes the duty to kill witnesses if possible. However as he is experienced in great scale fights and battles he has still a pragmatic view to go morally questionable tactics if they are necessary, though he still is inclined to hold such usages of tactics as sparse as possible. Outside of fights he is though more easy going where he likes to walk through the place he is summoned and see the way of living of the local people where his normally rather stoic-serious expression is greatly softer.
So if summoned in Japan he would find a liking in the anime and manga try to draw one himself. Also he enjoys that similar to in Persia there are takeaway kiosks were he likes to taste it though he himself. In a sense it can be said that in such situations he behaves like a youngster of his age.
Demeanor towards Master:
He is towards his Master initially wary and cautious. Essentially he treats them like he treated at the start of his reign a Parthian noble. So in a rather wary and cautious way, yet he trusts them to a degree and treats them with some respect. However after awhile he likes to exchange their views and holds conversations with his Master to try to gain a mutual understanding as he'd prefer to get along if possible. So should his Master be a man or woman of skill and knowledge in the magical area or martial one he would be fond to trade their knowledge. Also should his Master be themselves rather young he would like to take a directly friendly attitude where he would rather openly smile and treat them more familially. So if they should be in the need of it he would for them be an open listener and a shoulder where they can lean on and perhaps let loose their tears.
Should his Master be a young beautiful female he may attempt to establish a romantic start of relationship, if he finds her personality as appealing as her appearance. Should she have instead already a hidden crush he may switch between a protective older brother to one that likes to tease her. Furthermore he has a very good compatibility to motherly Masters.
However should the attempt to a common ground or understanding not be possible he may retain his distrustful demeanor and treat his Master instead as ally but not more beyond the acknowledgment that he has to ensure their safety, and he will only listen to their advise if they are necessary but their commands are another matter.
His own wish would be to be summoned with his full might as Heroic Spirit in the year 590~ as the tumults started that weakened the Sassasnid Empire, to end them, reunite it and to annihilate the Islam: the "evil" that destroyed his country before it came into existence. However if he grows attached to his Master he may instead try to use his wish for their luck.
Dialogues:
The other Sassanid Rulers and other persons:
He has towards Ardashir and Shapur the First the greatest respect as These two founded the Sassanid Empire. Furthermore he holds great pride in to having made the name "Shapur" proud. As he caused the first Golden Age of the Sassanid Empire.
Towards the Shahs after him he has a varied opinion. Some he respects for their skill and expertise, while others he despises for their failures. especially
Bahram Chobin, who he consider as great traitor.
Kyros the Great:
"The great founder of Persia, Kyros the great it is an utmost possible honor to meet you. Damn where is a pen and tablet eh I mean paper!? I am sorry great founder, how would it be if we talk over a delicious tea?"
Arabic Servants:
"Those desert vermins, had I known what danger your remains posed I would've fully exterminated or at least conquered Mecca and took control over it, to ensure that this movement never had an opportunity to build itself."
Zenobia:
"S
orry but I don't side with Arabians on principle. Though had I knew that you were such an illustrious and good queen perhaps I would've changed my decision."
Boudica:
"So the Romans where also attempting to conquer your country? it pains me to hear what they did to you and your family. May you want to speak about your culture and tell you from mine? I would be curious about your spirituality of your country and your values Boudica?"
As fellow enemies of Rome they naturally get along well, as they like to exchange their cultures, like as one day Shapur tried to make a cake but had a small mishap, but she was rather amused than annoyed.
Minamoto no Raikou:
"What? Sorry it was only once a slip of the tongue so you don't need to buy it such attention. Really Miss Raikou, really."
Ever since he once called her mother by mistake she has been hooked. He tried to stop her but couldn't withstand her maternal force.
Raikou: "At first I thought you were a naughty delinquent but you are a good child. Can you please look after Kintoki if I am not around, because he recently hangs around those shady insects."
Jimmu:
"The first Tenno, so the first ruler of Japan. Although you can't expect that I bow to a foreign King but you indeed are worthy of great respect as you have a similar dignity as the great Kyros. would you be willing to chat over a mint-tea?"
Arbre du Tenere:
"Okay, hold a sec. You sweet thing lived in the area of the desert crawlers? Sorry the you knew were another culture I understand. How may I help you with the next grocery deliveries and give you a hand in the kitchen?"
He is after this misunderstanding quiet embarrassed as he made her sad and drew the anger of many Chaldea Servants. So he is concerned about her although she has forgiven him already.
Kay Kawus:
"A legendary Shah of the Kayanian dynasty, I am greatly honored. May you be willing to answer me some questions?"
Nero:
"W-what the? You should be a Roman Emporer and the one that had burned down Rome. I have heard many stories in my life but you aren't the type to be able of such an atrocity. In fact you are rather adorable. Why had the populace of Rome something against you?"
He is initially irritated that this Nero is so different than in the record. Though he is unaware what bad singer she is, as he was a spectator of one of her song entrances but due to either a miracle or other outside intervention she hit the right notes and her singing was beautiful. So he visited her songs quite regularly and every time he was present she was a successful songstress like she imagined and despite that she won't admit it she think of him like a good luck charm. So she after getting to know him much better gets along quite well.
Dialogues from others:
Miyu Edelfeit: "I dont know why ,at first i thought of him as scary and Cold but after a awhile does he remind me on my Oni-san."
Nero:" I thought you Persians are all so hostile and unfriendly but you are a quite friendly and nice Guy ,you know what i will give you a tour through Rome one Day~!"