One idea could be the SI (Self - Insert) character using their gamer knowledge to unlock unique powers in the Highschool DxD universe. For example, they might figure out a way to level - up their devil or angel abilities like in a game. Another plot could involve the SI character forming a special team with the existing characters in the series to compete in some sort of supernatural gaming tournament within the DxD world. This could bring in new challenges and alliances.
A possible plot is that the SI gamer gets transported into the Highschool DxD world but discovers that their gaming skills are directly related to their magical abilities. So they start training like they would in a game, grinding levels by doing quests for different factions. They could also introduce new gaming - inspired spells or techniques that no one in the DxD world has seen before, which would make them a target for some and an ally for others.
The SI character could be a gamer who is actually a reincarnation of a powerful being in the Highschool DxD universe. Their gamer instincts help them recall their past life's knowledge and powers slowly. They then use this knowledge to not only become stronger but also to change the fate of some of the characters they befriend. For instance, they might prevent the death of a certain character by using their knowledge of future events from their gamer - like precognition skills.
Chapter 911, "You Have Three Children?", is the clearest early answer because it turns Jiang Buchen's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Jiang Bufan stood still, with his eyebrows furrowed, as if he was...
Chapter 844, ""Lang", is the clearest early answer because it turns Chixia Village's situation into a concrete plot event. A useful checkpoint is the way the scene starts with He had been married, but his wife disliked his disability and...
Chapter 483, "Why Does a Pig Eat M9?!", is the clearest early answer because it turns Huoxiang Zhengqi's situation into a concrete plot event. Early on, Wilderness Survival Day 11, temperature 31 degrees, wind speed.... By the end, Jiang Yan had apparently gotten used to it too..
Chapter 622, "Actually Tie Her Up?!", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event. The chapter gives readers a real answer by opening on Watching the uncommon expression on the man's face, Su Yinwan was...
Chapter 810, "I'm Waiting for Death", is the clearest early answer because the violence around Seeing Jiang Bufan becomes final instead of hypothetical.
Chapter 899, "It's actually a seal script?!", is the clearest early answer because it turns Rong Junsheng's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Cheng, with his head dizzy, was pulled into the courtyard by...
Chapter 726, "She Has Already Tried to Keep a Low Profile", is the clearest early answer because it turns Weibo's situation into a concrete plot event. It opens with Su Yinwan was using the money she had recently acquired to boost... and closes on After some thought, she took out her phone..
Chapter 851, "Peace Charm", is the clearest early answer because it turns Shi Lei's situation into a concrete plot event. A useful checkpoint is the way the scene starts with She initially came with the expectation of becoming the Gu Family's...
Chapter 685, "Defense Value Skyrockets!", is the clearest early answer because it turns Mr's situation into a concrete plot event. It opens with The scene went live on Weibo right then. and closes on How could he not be furious?.
Chapter 657, "The Richest Man Becomes a Hardcore Fan?!", is the clearest early answer because it turns Zhou Xu's situation into a concrete plot event. The chapter gives readers a real answer by opening on Zhao Lang had arrived in the Capital in the early hours of the...