Disclaimer: I don't own High School DxD or it's related concepts and characters, but Ichiei Ishibumi and his affiliates do.
Fantasy Made Real
Upon defeating the Hero Faction of the Khaos Brigade and rescuing the leader of the Youkai residing in Kyoto, Issei Hyoudou was specifically requested by said leader, Yasaka the Nine-Tailed Fox Kitsune, for a private meeting between the two of them the day before he had to return to Kuoh Town. As he made his way to her home, Issei was internally conflicted. While it seemed unlikely that he was in trouble for something he had no knowledge of, he couldn't help but think that Yasaka probably wanted to reward him for protecting her daughter, Kunou, and rescuing her in the exact way Issei imagined that she would, which was both stimulating and scary at the same time. As much as Issei wanted to truly become a man, the events that shaped him from an ordinary Human into a Reincarnated Devil hadn't left his mind in spite of all he had accomplished.
Once he arrived at Yasaka and Kunou's dwelling and was escorted to the former's bedroom, Issei could feel his heart pumping as he ultimately brought his hand to knock on the door.
"Come in, Issei." He heard Yasaka say from the other side.
Gulping, Issei opened the door to see Yasaka still in her golden kimono and smiling kindly, if flirtatiously, at him as well as a perfectly made futon which gave Issei the thought that he was wrong to think Yasaka would thank him in an intimate way.
"Is there something wrong, Miss Yasaka?" Issei asked in uncertainty about what she had in mind then.
Yasaka chuckled lightheartedly. "Oh, nothing at all, Issei, and please just call me Yasaka. I just thought I'd have you be here so that we could talk."
"Uh, about what?"
Stepping towards him, Yasaka said. "Allow me to first say "thank you" for watching over my daughter and the role you played in my return to her."
Scratching the back of his head sheepishly, Issei attempted to laugh it off. "Well, that was no trouble at all, Yasaka."
He was then surprised when Yasaka hugged him. "Secondly, I was curious why such a romantic young man as yourself is reluctant to reciprocate the love others have for him." She added with a sympathetic note in her voice.
"It's, uh, complicated." Issei stammered.
Smirking to herself, Yasaka then said. "Well, perhaps a fun deed mixed with good words will make you feel better."
Feeling his butt pinched, Issei yelped in shock before Yasaka kissed him on the lips which he soon came to return.
Guiding Issei to the futon, Yasaka began to strip him out of his Academy uniform with a particular focus on his pants and underpants. Once she pulled his personal "sword" from out of there, Yasaka noticed how upright it was from just a kiss and its own exposure which aroused a chuckle from her. "Just go with it, Red Dragon Emperor, and remember that you're supposed to pleasure me as I do you." She advised with a wink before she began sucking on the dick in front of her.
Issei gasped as she played with his balls and made him cum into her mouth. Yasaka soon took off her kimono, exposing her pink-colored nipples and golden trimmed pussy, and brought Issei's erection back up and running. With a beckoning gesture of Yasaka's finger, Issei knew what he had to do, considering he daydreamed about it. Taking both nipples into his mouth with one hand, he sucked hard as he used his free hand to rub her Yasaka's vagina which made her moan in pleasure. Before she climaxed, Yasaka panted out. "Issei, you might want to be ready to relocate your mouth."
Getting the hint, Issei released her nipples and switched to her hole to suck up all the cum. Once that was taken care of, Yasaka then stood on her arms and legs before telling Issei. "I'm afraid with everything going on, we'll have to make this quick, love."
Seeing how she was swaying her behind towards him, Issei nodded in acceptance and then asked with a shy smile. "I know you're a Nine-Tailed Fox, but can I at least ride you like a horse?"
"Oh, never thought about that before." Yasaka cooed in interest and swayed her ass one last time. "By all means."
With her permission granted, Issei grabbed her derriere with both his hands and brought his cock into her hole there. As Yasaka gasped in ecstasy, he then grabbed hold of both her ponytail in one hand and her longest literal tail in another which Yasaka gasped even harder. With Issei pumping her repeatedly, he then felt that he was about to blow. "Yasaka, I'm ready!"
Yasaka nodded her head in her lustful daze. "Just remember, Issei, when you grab a woman's heart, you're supposed to take responsibility no matter what!"
"Right!" Issei shouted as he released for the final time that day.
As they both panted in exhaustion, Yasaka was quick to guide Issei back on his feet and they both got dressed again. Kissing the latter's forehead, Yasaka told him. "Thank you for the warm memories, Issei. Do you need some help getting back to your class?"
Thinking it over, Issei shrugged in acceptance. "That doesn't sound like a bad idea. And I'm grateful to you, too, Yasaka. I'll be sure to remember what we did and what you told me for the future."
The two then exited the bedroom.
Back at Kuoh Academy after his time in Kyoto, Issei met up with his Devil Peerage King and Occult Research Club President, Rias Gremory in the ORC Building's meeting room.
"From what I understand, you went through quite the experience on your school trip, Issei." Rias started offhandedly and from the way she sounded, Issei knew she wasn't just talking about his encounter with the Hero Faction.
"It was pretty enlightening, Rias, I can tell you that much." Issei shrugged with a concerned smile, even as he addressed her casually for the first time.
Her attention grabbed, Rias stared at Issei in bewilderment. "Did you just-"
Her question was soon interrupted when he hugged her and added. "I'm sorry I was too scared to say or do anything, Rias. After what happened with Raynare, I was afraid that I'd eventually get rejected or something. But I should've known better about you, Asia, Irina, Xenovia, Akeno, and pretty much everyone else. Want to start over again?"
Smiling happily with a blush, Rias hugged him back. "I like the sound of that, Issei."
Wanted to do this since I first saw Yasaka's anime debut. Hope I did all right.
Anyway, I just want to add that I don't have any full-length story plans for High School DxD at the moment anymore. It struck me as difficult that I'd have to find a good spot in time for an AU possibility when DxD doesn't have a clear timeline compared to Dragon Ball and Fairy Tail among other things, so I plan on describing the non-Devil Issei ideas I thought of with pairings in a soon to be made High School Dxd Alternate Paths sort of thing.
Be on the lookout.