Spoiler.
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Arty is EXTREMELY masochistic. She likes being ignored, trampled and others but most of her request are ignored by Leo and she is also afraid of Elsie (only when Elsie is serious) there is also that scene in the novel where she is turned into a spear to pierce Erebus (because pegasus are beings of purity which means they are the enemy of Erebus and they could inflict damage to him) as she pierce him, leo lets go so she stayed to Erebus body to do more damage (erebus can't heal the damage she's done while she is in his body) and Erebus holds her and tried to destroy her by using his ability thus he inflicts pain to make her let go but she just laughs and said that "I love this pain, more" and Erebus gor bewildered by her craziness and when Leo got her back, Erebus ask Leo "whats with your pegasus" and Leo answered "not even me can control her"
She is so different with the first pegasus that Leo (Kyle) contracted which is the king of the pegasus (Albus). Albus is a lot more mature and dignified as opposite to her that then they meet. Albus even begs Leo to change his pegasus to a different one as he doesn't want to acknowledge Arty as a pegasus
And for context, Arty is a mature pegasus unlike fiora and kiruan which are both kids. Pegasus, fairy and Phoenix are the top of the summons that are difficult to obtained and are the goal of summoners as they are rare and requires more summoning skills to handle and that they could also reject summoning. Leo just so happens to have an obese pheonix, mischievous fairy and a pervert pegasus which has 0 dignity whatsoever. (Btw the pervert, obese and mischievous are all novel's description of them, i did not made that up)
Well that depends on. For me tho, the story and the characters are so good.
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As the story progresses, people might think it became harem as oppose to a normal action story but i think as leo's past gets reveal a lot of the characters (those that knows) wants to be the support for leo especially that his one and only goal is the conplete defeat of Erebus. It became his life goal and even if he achieve that he has no other goal and he really has nothing to do after that. He (Leo/kyle) is a hollow person to begin with, in the past he is an orphan and live to became a mercenary, all the things he cared left him and that learn to never aim to have anyone by his side since they will all leave in the end and nobody taught him the nomalcy of life beacuse it wasnt possible due to the world ending and in this current life, those that knows who he is just wants to be his support as they know the heavy of a burden that he is carrying (its like atleast 3 people who like him romatically) the rest just wants to support and and hovers around him because he is their leader and their goal is to get acknowledge by him. And leo on the other side never look at them romantically, he just wants them to be better enough that they won't die is worst comes to worst.
Heck, Carl has a better love story than him and he even has 2 girls pining for him lmaoo and he got a girl officially, he reject the other one and Leo accidentally witness it that Carl even asked Leo to make it rain
I feel like you will get a better understanding of the characters (and the so called girls in the harem) if you read the novel. And if romantically speaking, Leo mentioned that he has a person that he love/admire (she is a dragon (not lysinas) and the one who taught him magic and summorning and is part of the mercenary group that Kyle was part of before Erebus even existed)

Arty is drawn so pretty but my image of her is gonna be soooooo ruined