Issei was just walking home from school as he got shocked from the information Rias Gremory had given him. What's more, is what Yuki-sensei told him after the discussion ends.
~Flashback~
Issei was shocked from the revelations that he's indeed a devil now. Right now he's in a dilemma to either chase his dream or be careful of what happens to him next from he could tell from what Rias told him, the devils had a lot of enemies so even though she said the Gremory care about their servant a lot would it be enough for her to sacrifice her all for him ? He had read a lot of books regarding devils and it seems to him that the Gremory hold the Sin of Greed. Specifically greed for their servants, they're like a dragon hoarding for gold, it's no matter how small the amount is they never let anyone took anything from them.
And from what he could tell Sona Sitri seems to hold the sin of pride as she held her servants in high esteem more so than herself. But the mystery was who is Yuki-sensei and what does her plan in interfering in Rias and Sona territory. She's strong to strong in fact from the pressure she exerts and from what Ddraig told him about her when she exerts a portion of her power.
{Flashback in a flashback XD}
When Issei and the others leave the ORC building the suddenly felt a strong pressure on them. They fell down to their knees and wanted to kneel but after a while, the pressure dissipates leaving them confused. Even though they wanted to find out what it was they decided to ask their respective king tomorrow. The others disperse, but Issei stayed frozen.
[Issei's Mindscape]
Issei saw a red dragon shivering quietly while muttering 'No way, there's just no way' This is the red dragon of domination, the Welsh dragon Ddraig. Issei wondered why he would be pulled here or why is Ddraig shivering where the cause is the pressure so it's quite possibly because of fear.
"What is wrong Ddraig ?" Issei asked while patting the wing of his partner. Ddraig then stopped shivering and looked towards Issei. Then suddenly a bright red light blinded Issei eyes but what comes after shocked him there's a red-haired loli, sobbing and her black eyes were becoming red. Issei was shocked that the almighty Welsh dragon was actually a female a loli one at that and now she's sobbing in his arm. "Shuush, it's okay I'm here," Issei said while rubbing her hair trying to comfort her.
Ddraig the calmed down and then said, "Thanks partner I need a person to lean to." Issei then asked so "why do you cry ?" Ddraig ponders thinking whether or not she should tell Issei about why she did so. Issei was anticipating an answer calmly if she didn't answer it then he didn't have to be sad as they had just been together for a while and it's hard to trust a stranger. But to his surprise, Ddraig actually answered his question.
"This is the secret in which we the heavenly dragons had to save guarded for a very long time, me and my rival... No my twin sister Albion." Issei was shocked by how much his partner trusted him but when he heard the second part 'Wait Ddraig and Albion were twins so why do they fight each other and Rias never told him about the red dragon of domination and the white dragon of supremacy being related even more so being twins.' Ddraig seems to notice the shock in Issei's face she giggled a little then continued.
"Yes Albion is my twin sister and we were born at the exact same time. We had the same mother, our mother left us a long time ago so we needed to fend for yourself. We never had a father as to when dragons were born we could already see and think for ourselves but we couldn't talk. From the day we were born, we never saw our father only our mother taking care of us for a while and then left us in the forest because she's being chased by her enemies. We never know who her enemies were but she was already really strong back them surpassing mine and Albion's power level combined." Issei then started to piece together the puzzle pieces but still, he's really shocked as Ddraig mother had power level surpassing him and Albion's combined together so how terrifying are her enemies.
The other possibility is that while she's strong she's more combat oriented and couldn't protect her babies while fighting thus leaving them and escaping far away to ensure their safety. Anyway back to topics, "We were really close as what a normal twin would look like. We also set our goals to find our mother, but it all because of a little thing which started our rivalry and that's...."
Damn it WN I already wrote over 1.3k words for this chap but it got deleted for some reason and I'm lazy to write more and yes this is a filler chapter.