High school DxD - issei little sibling

Even by his own admittance Issei is an unintelligent and straightforward individual, having extreme trouble grasping even simple concepts when they're explained step-by-step and repeatedly to him, with his tremendously perverted and lascivious nature being the greatest characteristic of his personality. Issei easily indulges in lewd fantasies, being obsessed with female breasts and a desire for a harem, traits he openly admits and makes no effort to hide, a characteristic that he is, in fact, proud of. This has caused him to be instantly labeled as a pervert among the girls of Kuoh Academy and has gained him notoriety for being one of the members of Kuoh Academy's Perverted Trio.Despite his outward personality being unpleasant to other characters, Issei is actually courageous, selfless and unwaveringly determined to protect those who are important to him, despite almost dying by the hands of his opponents. Quite regularly, this bravery can be amplified by having the situation connected to his lustful interests, blowing away any trace of fear.

As noted and pointed out by Koneko, although he is the weakest Red Dragon Emperor, Issei is the kindest among them, as unlike his predecessors, Issei is not power hungry. This can be seen when he was the only one who did not succumb to the Boosted Gear's curse, not having been consumed by the hatred, the thirst for power and destruction that consumed all those who came before him. Due to his great kindness, Issei is also very caring, "putting his nose into other people's business" as he helped Yuuto Kiba, Koneko Toujou, and Akeno Himejima overcome their fears and hatred of their difficult pasts. Due to this, he gained strong friendships with his comrades and affection from most girls of the Occult Research Club, as well as a strong sense of friendship with higher-up Devils like Rias' family; they have told him to use the same titles for them as Rias (Father, Mother, Brother, etc.), yet he still remains the same. Issei's kindness also have a positive influence on others including former enemies. When Issei suggested to Cao Cao to use his True Longinus to help and protect people, Cao Cao acknowledged had he and Siegfried met and befriend Issei earlier, they would not have ended up becoming terrorists in the Khaos Brigade. Another sign of his kind nature is that despite wanting to lose his virginity, Issei refuses to take advantage of women when they are upset, even if they themselves are willing to. This happened when Akeno Himejima appeared in front of him naked and wanted to have sex to forget about her sad past and her father. However, Issei refused, knowing it will just hurt her more, and put her clothes back on and hugged her to comfort her.

He has a habit (as mentioned by his mother) of not forgiving himself if he does something wrong: always saying sorry on instinct if said thing is mentioned, and showing an expression of pain and regret. He is also fiercely loyal to his comrades and is always willing to stand up for them. After his murder by Raynare, Issei had developed a fear of admitting his feelings to the girls in his life, as he thought it would cause them to reject him. This would also cause him to become oblivious to the feelings of the girls around him (save for Rias after his confession), often believing they are simply teasing him or even leading him on as Raynare did. He acknowledged that this would never happen, but it was still an intense fear. Even when the girls of the Occult Research Club such as Akeno or Xenovia Quarta proposition him into making love to them, Issei would always initially hold himself back, as he would sometimes look at them with a frightened gaze, a fact which Akeno, Asia Argento and Koneko Toujou later noticed. His fears were finally brought to attention when Akeno, Asia, and Koneko confronted him alone and helped him by getting him to admit his feelings and assuring him that they would always love him and so would Rias. This inspired him to finally confesses his love for her which she reciprocated, effectively helping Issei move past his fears. Even with the knowledge that the girls do have romantic affection for him, he still has problems acknowledging some of their ongoing rivalries, an example being who gets to sit on his lap. Also, despite his otherwise intense lust and love, Issei seems to still share the "denseness" and "gutlessness" of the average shonen harem protagonist, and on an even higher level, with him constantly finding excuses not to give in to the girl's active attempts to seduce him for over a year, even claiming to have his mood ruined when another of the girls stumbles upon and attempts to join in on the attempt, and still being completely unable to recognize when another girl clearly likes him. In reality, Issei has an innocent side; he is a boy who yearns for love and a true relationship, a side which he only shows to women who can see past his perverted exterior and love him for who he is and who he, in turn, has affections for. He shows this side to the girls of the Occult Research Club, for instance on his date with Akeno or when Rias takes him out on dates. Initially, after reincarnating as a Devil, he set about his desire for a harem as his initial goal, by having his peerage become his harem. After the Rating Game against Sona Sitri and Genshirou Saji, he slightly changed the goal to having a harem Peerage that wouldn't lose to anyone. Among his other goals include competing in Rating Games and making Rias the Champion of the Rating Games by becoming the "Ultimate Pawn" alongside Yuuto Kiba, who promised to become the "Ultimate Knight" with him and his desire to become the Champion of the Rating Games himself after he obtains his own Peerage. He is also deeply invested in his rivalry with Vali Lucifer, his Heavenly Dragon counterpart, as Issei promised to get stronger and defeat him, with the both of them reaffirming their promise to fight each other some day multiple times during the series and Vali suggesting that Issei create his own team like Vali which is different from his peerage. Their rivalry would heat up after the both of them enter the Azazel Cup, with Issei creating his own team, Team Red Dragon Emperor of the Blazing Truth, to try to win the Azazel Cup and defeat Vali during the tournament. After the two of them passed the preliminary rounds, the two expressed their desire to continue their initial fight as the both of them promised not to lose until they meet each other in the Cup. As revealed by Shiva, Issei is a pacifist with a deep desire for peace, an attribute theorized to have been further strengthened by him being the "child" of Great Red and Ophis and being affected by their will, as Issei seems incapable of realizing his dream of becoming a Harem King, living happily with the women he loves until he obtains peace with his own hands. Due to experiencing intense fights in which he experienced great suffering to the point he nearly died on several occasions, like Azazel and Sirzechs, Issei has become dedicated to pacifism as he affirms his desire to create a world without war and protect his companions even if his enemy is a God.

This will be a au of the same high school dxd instead this time issei has a younger sibling since he's the oldest in his family where it takes place in the same anime or light novel

Issei is the Pawn of Rias Gremory's Peerage and a member of the Occult Research Club. After the Evil Dragon War, he was promoted to the rank of a High-Class Devil, becoming the King of his own independent peerage, and is one step closer to fulfilling his dream of having a harem and becoming a "Harem King" but has a younger sibling(or you can make it a step sibling)