Write a descriptive, interesting and exciting short story in the form of a lengthy chapter of a crossover fanfic between Shinmai Maou no Testament/Testament of Sister New Devil, Nakaimo: My Sister is Among Them! and High School DxD with plenty of dialogue and exposition, in which Issei Hyoudou is actually an alias for Shogo Mikadono, the heir and future head of the Mikadono Group after his father Kumagoro Mikadono goes into a coma. Shogo attends Miryuin Private Academy in Kuoh, under the name of Issei Hyoudou to have peace and anonymity during his time at school and to prevent his father's enemies from finding him. 
Unknown to either the staff and teachers of Kuoh Academy, who are aware of Issei's secret, or even the Mikadono clan or the higher ranks of the Mikadono Group, Shogo/Issei is actually Basara Tojo, former child prodigy of the secret Hero Clan hidden deep in Kamakura and son of the legendary hero Jin Tojo, who has now become a wandering mercenary after he [Jin] was expelled by the Hero Clan.After rescuing his younger half-sister Yuki Nodoka from being killed by a disgraced ex-hero who had been possessed by the spirit of his current sword Brynhildr as a young boy, Basara passed out from defeating the ex-hero and hit his head on a rock, causing him to lose his memory. 
Before the forces of the Hero Clan can come to retrieve him, Basara was taken in by the forces of the Mikadono Group who were attracted to the scene by the noise of the battle and brought to one of the Mikadono Group's private hospitals, where he was visited by Kumagoro, who thought that he [Basara] was Shogo, not knowing the real Shogo was dead. 
Basara then grew up as the heir of the Mikadono Group, thinking that he was Shogo and preparing for his eventual ascension to the position as boss of the Mikadono corporate empire, until he was spotted by one one of Jin's agents and reunites with his true father. He is surprised to learn that he is actually a member of a association of samurai that managed to survive the Meiji Restoration and has dedicated itself to hunting down demons, yokai, ayakashi and other supernatural threats while protecting Japan from things that go bump in the night, but is able to recover from his shock and manages to regain his sword skills while keeping the truth about himself a secret from his de-facto foster family in the Mikadonos and the Mikadono Group. 
By the time Basara aka Shogo Mikadono is in his second year of Kuoh's high school division as Issei Hyoudou, he has managed to reclaim his swordsmanship skills and master his Onmyōdō arts while preparing himself for his eventual rise as the head of the Mikadono Group, all while pretending to be a idiotic pervert obsessed with women's breasts as Issei. The plot of the chapter would involve Basara as Shogo Mikadono relaxing in his spacious apartment in the suburb of Kuoh that was given to him by the Mikadono Group, before a knock on the door startles him out of his thoughts. When he goes to open the door he is greeted by the upset faces of the silver-haired first year at Kuoh and infamous nerd, the short and sharp-tongued young girl Mei Sagara and Sagara's older cousin, the shy and reserved but also outgoing and loud redheaded President of Miryuin Private Academy's Economics Club, the bubbly Mana Tendou.
The two girls have come to visit Basara/Shogo because of his acquisition of a vast harem due to him becoming the teacher's pet of the popular and well-liked English teacher Himekami Lizel, and feel somewhat jealous because they have always had feelings for him but were afraid to admit it until now. Mei and Mana have also paid a visit to Basara due to Mana's true identity being Millicent Gremory aka Mio Naruse, the daughter of Sirzechs Lucifer, one of the Four Great Magical Kings of the Underworld and Mei being her bodyguard, Maria Naruse, assigned to protect her [Mana/Mio/Millicent] from Sirzechs' many enemies in the Underworld, which lead to Basara's true father Jin taking them in under his wing and adopting them as his daughters. The two girls' unannounced visit to Basara/Shogo's apartment is so that Mei can inform Basara/Shogo of the undertakings in the underworld while also confessing her love for him [Basara/Shogo] along with Mana/Millicent/Mio. 
After dealing with business, Mei/Maria and Mana/Mio/Millicent confess their love to a surprised Basara/Shogo and cuddle up to him, with Mana/Mio/Millicent kissing him on the cheek and Mei/Maria engaging him in a passionate makeout session. The brief moment of tenderness is interrupted by a now older Yuki Nodoka and Basara/Shogo's adoptive younger sisters from the Mikadono family, the black-haired, green-eyed traditional Japanese beauty Konoe Tsuruma and the headstrong, feisty brunette Miyabi Kannagi, who have been searching for Mei/Maria and Mana/Mio/Millicent and get jealous when they see the two other girls cuddling up to Basara/Shogo. Konoe and Miyabi confess their love for Basara/Shogo along with Yuki and start cuddling up with him on the couch too, with Yuki Nodoka reluctantly joining in the whole thing after Miyabi reminds her she [Yuki] loves Basara/Shogo as well.
The chapter ends with Basara/Shogo and the girls enjoying their time with each other on the couch, unaware of the fact that they are being watched by Shinji Kanzaki, the former Pilot of the EVA-Unit 01 combat mech designed to fight the monstrous Angels under the alias of "Shinji Ikari" and the "Black Sweeper" of Tokyo-3 due to his [Shinji Kanzaki's] one-man crusade against small-time criminals and corrupt corporate executives in Tokyo-3 after escaping from the clutches of NERV after the fall of the Angels. Perched safely on a tree, Shinji observes Basara/Shogo and the girls of part of his harem enjoying the presence of each other, taking notes and taking pictures of Basara/Shogo and the girls of Basara/Shogo's harem. Shinji shakes his head as he watches Mana/Mio/Millicent push herself up against Basara/Shogo, causing her large breasts to squish against Basara/Shogo's body while Maria/Mei pulls down the neckline of her dress to show her large bust as well. 
After taking his notes, Shinji comments that Basara/Shogo is going to have a lot of children quite soon before jumping off the tree he [Shinji] is perched on, and teleporting away to his [Shinji's] nearby base. 