Most people might recognize him, if you are currently not caught up, as that yankee asshole from an earlier episode. He had a fight, ate a bunch of food, and then claimed he was going to be neutral or at least not pick fights with the protagonists. Well, yeah kinda. We know that Yuuya hails from a fighting/underworld series known as Heisaku underground -dark night-. He can summon another being so this is most likely a summoning battle-type manga. He is the "rival" to the protagonist. When we look purely at his design, it is very clear that he resembles Shou Minazuki from the series Persona 4 Arena Ultimax. It is surprising how much these two are alike if you were to place the colors of Yuuya over Shou. The resemblance is blatantly there. Both characters as well sport swords, but Yuuya has one and Shou has two.

However, their backstories are very different. While Shou is/was the subject of persona experimentation, Yuuya is not. Yuuya is more of a fighter and his gang fights a rival gang within his own manga for territory in a city where crime appears to be high. If there was a series that is similar in feel, it would have to be Holyland by Kouji Mori. In it, groups of gangs fight for territory to protect their own "holylands". Yuuya has already pointed out that his rival is the main character of the story, so there is a good chance then that Yuuya is not Yuu Kamishiro, but rather Masaki Izawa. Though this time though, the medium is boxing and karate rather than swords. Either way, he's a well-thought-out character.

Sure, there are plenty of series that shove a young boy into a robot and either a drunk parent, crooked parent, or guardian has said "Shinji get in the damn-" err we mean "It's time for you to save humanity!". He's got a giant robot, it's a bit unwieldy at that, and Rui has a constant aversion to getting into said robot. He also has phrases like "I'm tired of everything not making sense" and "No matter what you say, I am not getting back in that!" Let's think of a mecha series that has a main character like that!

Rui is clearly an inspiration from Shinji Ikari from the Evangelion series.

Shinji is a bit reclusive in his feelings and tends to get down A LOT. However, Rui is kind of different, and let's also not forget how fast he kicks ass when the government crashes his creator's house. When we think of other characters from other mecha series, another big franchise that comes to mind is Gundam. Rui could just be an inspiration of Kamille Bidan from Mobile Suit Zeta Gundam.

Let's talk about the elephant in the room, Celestia Yupitilia. Hailing from the series Seireiki Souykyoku Vogelchevalier, this fiery redheaded girl controls a robot known as Vogelchevalier until Gunpuku no Himegimi destroys it. Skilled in sword fighting, she at first rejects her situation before slowly beginning to accept it. Before proceeding further, we should say that Celestia could be an amalgamation of characters. She definitely gives us Stella Vermillion vibes from Rakudai Kishi no Cavalry. She has a rather ample chest as well as Celestia does. However, there are no robots. The overall feel of Celestia's story leads us to believe that it could be an inspiration of Tenkuu no Escaflowne, but Hitomi is not really getting into the robot like it is clear that Celestia can. She could be Hikaru Shidou from Magic Knight Rayearth, but the overall feel of Rayearth is a bit different. Plus, we know that the backstory for Celestia is in the form of a light novel.

So, we need a well-endowed female character, good at sword fighting, and has some sort of fantasy element as Celestia is able to dole out orders to Vogelchevalier while not being inside it, it is from a light novel, oh and, if you have payed close attention, then you know that she has a male counterpart as well in her story who appears on the covers with her. This one was the hardest to piece together and the fantasy one is a bit reaching, we know, but there are no stories that fit the mecha theme. Celestia is most likely an inspiration of Asuna from Sword Art Online. Celenstina and Asuna both are amply chested, excel at swordplay, exist in a fantasy world, come from light novels, and on a certain level as Celestina softens, she becomes very likeable much like Asuna. The fantasy aspect is one of the hardest, but we do feel like this is an actual, solid resemblance.