Maybe Pit from Kid Icarus gets transferred to the school in High School DxD. His angelic nature causes quite a stir among the devils, angels, and fallen angels in the school. He could form an unlikely alliance with Issei to face the challenges that come with this new environment.
One idea could be the characters from Kid Icarus and High School DxD teaming up to fight a common supernatural threat that combines the mythologies of both universes. For example, a demon - angel hybrid that also has ties to the Greek mythology in Kid Icarus.
Another plot could involve the exchange of powers. Some characters from High School DxD might gain the ability to use the weapons or powers from Kid Icarus, like the Power of Flight or the use of the Three Sacred Treasures, and they have to learn to control these new powers while dealing with their own high - school - related drama.
The best chapter pointer here is Chapter 51, "The Great Lodging Competition". It opens with Oh, okay." After uttering two syllables indifferently, Jiang Li bent down... and closes on If I opened a bar here, wouldn't I become a savior?" Jiang Yan was....
The best chapter pointer here is Chapter 48, "All the Bitter Teas Have Been Taken Away". It opens with He Yun felt guilty for initially ignoring Jiang Li on purpose, and with... and closes on Besides, everyone's phones will be replaced with special smartphones....
The best chapter pointer here is Chapter 51, "The Great Lodging Competition". It opens with Oh, okay." After uttering two syllables indifferently, Jiang Li bent down... and closes on If I opened a bar here, wouldn't I become a savior?" Jiang Yan was....
Chapter 48 is the strongest chapter-level answer because it starts from He Yun felt guilty for initially ignoring Jiang Li on purpose, and with... and follows through on Besides, everyone's phones will be replaced with special smartphones....
A practical answer is Chapter 54, because it turns the idea into a concrete scene. The chapter opens with Five minutes later, the people of Chixia Village, who had received the..., adds pressure through Even the trolls in Jiang Li's live stream room were not very active..., and ends on She was.
The best chapter pointer here is Chapter 62, "There is Something Strange". It opens with Sitting on the edge of her bed, she pondered for a while before lifting... and closes on Jiang Li reached in, pulled out a piece of paper, and slightly raised her....
A practical answer is Chapter 34, because it turns the idea into a concrete scene. The chapter opens with Seeing that the public sentiment wasn't quite right, Su Yinwan felt..., adds pressure through Hurry up and start the live show, I can't wait to watch the universe's..., and ends on Now that.
The best chapter pointer here is Chapter 39, "Is This Book an Out-of-Print Buddhist Scripture?!". It opens with Qi Tianyu had been looking forward to watching Jiang Li's drama unfold. and closes on His original intention was just to make Jiang Li back off gracefully,....
The best chapter pointer here is Chapter 28, "Beaten Up Again". It opens with The next evening, Jiang Yan drove home seething with rage. and closes on Lili then kicked his knee hard..
Look to Chapter 50 for the clearest answer. It begins with [666, if good scores determine rankings, is Flash Change's production team..., keeps building through This is too tragic for this group of people.]" "[I'm dying of laughter,..., and lands on What kind of heavenly being had such a sour.