|Relative||Rino (Younger Sister)|
|Manga Debut||Chapter 7|
Ren (蓮,Ren), also formerly known as the Gentōryū(嚴濤竜; lit. Stern Billow Dragon) during her time at Nangokuren High School. Being the elder sister of Rino, Ren almost achieved supremacy at the violent school just before her graduation and had a fierce rivalry with Hatenko Meru, before befriending her.
Ren is a tall figure with grey hair tied in twin pigtails,and like her sister she also has green eyes, along with another tie wrapped around her left thigh (the said tie was given to Meru). She also often equips her sword as her main weapon.
As one of the toughest warriors, Ren is serious whenever she fought anyone stronger than her. That doesn't stop her to like things that a normal girl likes, and she even like some videogames (according to herself, she's supposedly good in tetris).
She also has a habit of changing her clothes during battle whenever her clothes are torn (even with the smallest tear). Despite her strong integrity as well as toughness, Ren has troubles with men due to her assumptions that men are perverse beings (which she claims that all men are trying to flirt with her, which she considered as vulgar). As a result, she cannot even speak to boys face-to-face and turns away from them, though she doesn't seem to have any problems with disrobing in front of Rintaro without any feelings of shame.
However, due to her friendship with Meru, she has taken an interest, if not a crush, in Rintaro, as well as his skills. She becomes flustered and shy everytime Meru jokes about Ren's will to see Rintaro as soon as possible.
At some point Ren joined Nangokuren High School and attended the school for 3 years. During her third year, she had fought against Meru and then became friends with her. Her fight with Meru would also inspired by the young Kyōka, who was a bookworm at her time. While surrounded by a bunch of thugs in a hidden ally and have them beaten without any effort, Ren would see Kyōka come at her to oversee the problem. Just as Kyōka would sense a brute is approaching from behind , Ren would tell her the instructions of dodge and counter attack against the Brute, which she witness the junior managed to give a brute a strong blow. Seeing that the book worm has the talents of a warrior, Ren would give her a compliment and encourage Kyōka to seek her own path while issue a battle against Kyōka.  Sometime later, Ren and Meru had fought one last time which result in a draw. Ren then introduces Meru to her sister Rino and have her work with Rino.
Encounter and Rivalry with the TigerEdit
Meru talks to Rintaro and Ayane about Ren and how she is the older sister of Rino and almost conquered Nangokuren High School. Ren and Meru were rivals for a long time and formed a friendly rivalry as soon as they find things in common, like phone straps and some games. By Ren's last year in Nangokuren, she challenged Meru to a last fight which results in a draw. Ren comments about how her younger sister, Rino, changed into a cold person with a goal to conquer Nangokuren, something that Ren wasn't able to accomplish. Knowing how shallow is the feeling of be alone at the top, Ren asks Meru to take care of Rino and they form the "Covenant of Hagen", with Ren's thigh tie as a symbol.
It is later shown that Ren began her covert return to the academy at the end of the Bakugyaku Festival, while watching Ayane's mentor from above, unknown to him. While pursuing clues to a underwear thief, Rintaro found Ren and mistakes her for the culprit. Ignoring Rintaro's questions, Ren would glide away with her blade and the chase begins until they reached the courtyard. She then sliced the statue in pieces and tossed a barrage of boulders towards Rintaro. While standing away from the rubble, Ren noticed that Rintaro escaped the barrage and assumed if his has used the "earthworm" skill. Even with Rintaro interrogation, Ren digressed Rintaro question while changes her clothes immediately after her's tore a little. After changing clothes, Ren told Rintaro that he stared too long while blushed.
During the conversation with Rintaro, Ren's receiving a phone call from Meru about her odd conversation before she hung up. She then tells Rintaro the reason for her to have troubles to men is because she thought men are trying to flirt her, which she considered vulgar. Ren was welcomed by all the girls in the academy and reunited with the Year 3 students (Misa, Choco and Kyōka). She then "helps" Rintaro in his search for the culprit behind the underwear theft by taking one of the underwears to him, much to Rintaro's displeasure.
After Rintaro defeats Marokichi by using his "eel", Meru arrived and asked Ren regarding her reasons to be in the school, to which she replies that she wanted to test "Rin-chan" as a worthy inheritor of the "Covenant of Hagen" and she wastes no time to tell she acknowledges Rintaro's merit. Ren asks him to take care of Rino, but threatens Rintaro to not make her sister his wife. Subsequently, Ren stares Rintaro with a smile without feeling uncomfortable, so Meru teases about Ren herself want to be Rintaro's wife, to what she blushes strongly. Ren recomposes herself and notifies she will come more often to Nangokuren (to see Rintaro, according to Meru). However, Rintaro told her that he would not be in the school for the summer vacations. Meru express her disappointment, Ren scolds her for bothering Rintaro and they start a fight, while Rintaro go away from them.
With the war for the royal seal between 2nd year and 3rd year students causing havoc, Rintaro stops Kyōka and Rino's fight and announces his application for Dragon. Along with Meru, Ren arrives to test him again and, once more time, recognizes Rintaro as someone worthy.
Meru - Her rival and best friend. They were the strongest at the school before the dragons. Finding they actually have things in common besides fighting, they formed a friendship and they had a last duel before Ren graduates from Nangokuren, forging the "Covenant of Hagen" for Rino's sake. Despite some mutual bickering, they are as close as sisters.
Kyoka - Ren was the main reason why Kyoka left her "honor student" persona to be what she is today. She convinced Kyoka to be herself for the first time in a while and they soon established a rivalry until Ren left the school.
Rino - Ren's younger sister, Rino looked up to her older sister, but, in some point, she became cold and basically turned away from Ren to accomplish what her sister couldn't to do: be at the top of Nangokuren. Rino's drastic change of attitude was what made Ren forge the "Covenant of Hagen" with Meru.
Rintaro - Meru sent Ren to the school to ask Rintaro's aid about the Gentoryu's problem with men. Ren's actual objective, though, it was to check if Rintaro was an worthy successor of the "Covenant of Hagen". Unimpressed by him at first, Ren soon witnessed Rintaro's prowess and disposition to go as far as he can for his friends. She not only approves him as someone worthy to keep Rino in check, but, as Meru noticed, Rintaro is the first man who Ren actually put her "fussy eyes". She can have a crush on him, but keeps defensive and ashamed about it. She wants to come more often to Nangokuren to see him, though.
Ren was once the strongest student at Nangokuren High School and had almost conquered the school.
- Expert Swordswoman: Ren was shown to be an excellent swordswoman and was able to hold her ground against Meru. When Ren returned to Nangokuren High School she displayed swordsmanship that utilizes spinning motions where she effortlessly destroyed concrete structures around the school when Rintaro had pursued her.
- Keen Analysis: Ren is very observant and perceptive as shown when she was the only one able to deduce the mechanism behind Rintaro's Sumibi Gyūkaku technique being similar to a stuck knife splitting a bullet when it's shot at the knife while all the other observers were puzzled by the technique's execution.
- Dual Headed Broadsword: Ren wields a dual headed blade that she was able to wield perfectly into a battle. The blade also contains a compartment that she uses to store her clothes for her to change with. Interestingly, her signature weapon also served as her odd transportation and glides away.
- Metsugen Ryūsen (滅嚴竜殱, lit. "Ruined Rigid Dragon Massacre"): 
- Ren's name is based on the water lotus, the Sacred Lotus, which is also a sacred icon of Buddhism.
- On the Tankōbon cover for the fourth volume Ren's eyes appear light blue, where as in the color centerpiece for Chapter 18 they are green.