Soren Noxis Siegreich/Relationships

Lucina Faustus
The first to join Soren's team in Kuoh Town, the two meeting the day Soren scoped out Kuoh Academy, the resonance of the Ruina Draco and Boosted Gear gaining the attention of her dragon, Naga. Shu was initially as neutral to her as he was most people, though as she held a Dragon Gear, and the fact Bahamut and Naga know one another, Soren agreed to teach Lucina of the workings of the supernatural world she wasn't aware of and help her grow stronger with her fledgling powers.

Soren was initially caught heavily off guard with Lucina's profession of her affection to him, but, despite troubled thoughts about it, accepted the confession and began dating her in the following weeks, coming to care for Lucina on an equal level and return her affections in kind, and holds her in high regard as one of the few people he can confide in with his woes and troubles.

Kuroka
Soren knew Kuroka at first as simply "Kuro", meeting her in her cat form, though he quickly found out she was a nekomata due to previous experience with such beings, namely Kira, a cait sith, a race distantly related to the nekomata/nekoshou. Soren regarded Kuroka at first as something of a presence that refused to go away, but didn't really mind her that much and is fine talking with her about most anything if it's brought up, though he never bought into her claims of being stuck in her cat form before she revealed her true form.

He doesn't mind how Kuroka likes clinging to him or using his lap as a pillow for her naps, and he even sympathizes with her plight regarding Koneko and how the Devils responded to her actions, as well as showing to gain a fondness for her, despite the occasional muttering of the trouble that would come his way if Rias ever discovered he was harboring Kuroka in his residence.

Astra Rose
Initially, Soren and Astra had a hostile relationship, though Soren was more dismissive of Astra's aggressiveness, seeing her challenges to him as pointless due to their difference in power. They often traded sarcastic remarks and vitriol whenever they met, Astra finding herself miffed by Soren's often contradictory nature and her inability to get a proper read on him.

But, as the two interacted more and got to know each other, Soren gained a fondness for Astra despite not knowing as much about her as she did him, stating he thinks she's "pretty cool" and has come to care for her as he does Lucina, though remains irked by her shows of affection and habit of coming onto him rather frequently, but always ends up rolling his eyes and laughing in the end.

Rias Gremory
To say Soren and Rias got along from the start would be far fetched. Their relationship was initially one of animosity, Rias holding a grudge against Soren for the ease in which he held off her peerage and his superior power to hers injuring Rias' pride, and Soren "interferring" with Issei's training irked her immensely, while Soren showed disdain for Rias as his initial impression of her was that she was no different than any other Pure Blood Devil, which he openly admits to having a disdain for.

Over time though, the two eased out the roughness of their relationship, Soren's bluntness towards Rias proving to help the girl humble herself a bit, while Soren came to respect Rias as she stood out from the usual Pure Blooded Devil, whom normally he can't stand. After the conflict with Riser Phenex, the two bury the hatchet and agree to be friends

Issei Hyoudo
Soren at first regarded Issei as little more than the person he had to observe, being openly annoyed with Issei's perversion to the point of aggravation, but as recompense for not being able to prevent Issei's near-death at Raynare's hands, he considers it his responsibility to help train Issei in how to use the Boosted Gear, and hopefully help his underclassmen think with his head rather than his nether regions.

Soren does however, come to regard Issei as a friend, shown in how he stops referring to Issei with his last name and instead his first name, and the two actually get along pretty easily whenever Issei isn't showing his perverted side, though Soren is rather miffed with Issei not catching on with Asia and Rias' affections for him.

Koneko Toujo
Soren didn't have much of an opinion on Koneko at first, only knowing of her as she and Kiba were sent to fight him when his cover was blown during his scoping out of Kuoh Academy. But, after deciding to train the Gremory peerage for their Rating Game against Riser Phenex, as with the rest of the Peerage, Soren put in extensive research into them to learn how best to train them, thus, he learned of Koneko's true nature and pieced together her relation to Kuroka.

Soren sympathizes with Koneko's initial misgivings about her powers due to experiencing a similar thing when he was younger and learning how to use the Ruina Draco, though his brutal honesty led to initially being too direct in stating Koneko's need to use her powers. After admitting to his mistake and talking extensively with her, the two reached a better understanding of each other, helped further by Soren's own knowledge on Senjutsu.

Soren shows to regard Koneko as something of a little sister in following days, Koneko herself showing to be more cheerful because of his help and even affectionate with Shu, Lucina hinting the small girl developed a crush on him.