Ddraig gets along very well with Issei, but later on when everyone starts calling him the Oppai Dragon, he becomes extremely depressed, to the point of crying, due to his reputation being demolished little by little. He has taken a great interest in Issei and admires his courage and tenacity, as well as the fact that he works hard and protects those that he cares about. He was with Issei when he died and he was devastated to the point that he cried and told Ophis that he was the greatest possessor of him, although he later returns from the Dimensional Gap along with Issei. Even when Euclid Lucifuge offered him a more powerful host by joining him, Ddraig quickly rejected his offer, saying that he wants to remain with Issei despite gaining the Oppai Dragon nickname and being the weakest of his past hosts, because he's a better host than all the others.
While there is a very small amount of interaction between the two, Ddraig has shown to have some degree of concern for her well-being, as he warned her to leave Issei when he was about to enter Juggernaut Drive to fight Shalba Beelzebub, as the power and destruction from that form would kill her. The reason behind this though is most likely due to Ddraig's knowledge that Issei cares deeply for Rias.
The other Heavenly Dragon and Ddraig's arch-rival. The two of them fought each other in the past which resulted in both of them being sealed in Sacred Gears. After so many years of fighting each other, both directly and through their hosts, both Ddraig and Albion have forgotten the reason as to why they started fighting, nor do they feel their usual antagonistic feelings for each other, which is most likely due to their current hosts. However, both realize that the battle between their hosts will happen eventually.
Ironically, the two have become closer due to the fact that they both have gained derogatory nicknames from the actions of their hosts. Both of them cry due to their broken pride, and each tries to comfort the other.
He was, at one time, a Dragon King and knew Ddraig before he was sealed.
Ophis at first only got curious to Ddraig's change from red to crimson but due to a series of events and with the help of Issei, they eventually became friends.
Ddraig has mentioned that Tiamat hates him, in the first he doesn't know the truth behind this. But in Volume 23 where Issei first met her and seeing Ddraig after many centuries did not remember the reason behind it. The reason is at some point in the past, Ddraig had borrowed Tiamat's treasure for his upcoming battle with Albion and was accidentally destroyed during the fight. Since then she has been chasing after Ddraig and his possessors for a long time, to retrieve her stolen treasure. Also although Ddraig is a Heavenly Dragon, Tiamat's anger is strong enough to bring Ddraig, a Heavenly Dragon, to cower in fear. He felt a great depression that he unable to return Tiamat‘s treasure after he was sealed in the Boosted Gear.
Ddraig doesn't seem like he wants to associate with Fafnir due to his perverted nature. As revealed in Volume 15, when Issei asked Ddraig about what he thinks of the Pantsu-Dragon King, he responded by saying that he didn't see anything.
Great Red and Ddraig have shown to communicate with each other and also work together to save Issei's life.
Since their first and second meeting to one another, Ddraig doesn't seem like Grendel very much. And knowing the fact that Ddraig sees him more brutal, crazy, and wicked dragon than he was in the past causes Grendel to return these feelings.
In the past they have seem to know each other, but like Grendel he hates and dislikes him very much, to the point that he mentioned his name in a light yet with anger toned.
Although the two of doesn't meet in person, the two of them does know each other. As Azi Dahaka knows him and Albion very well and calling them two, to their original names, in which they have discarded those names in the last two thousand years.