During their first meeting, Vali was on a completely different level compared to Issei, which made the latter feel inferior, prompting him to devote more of his time trying to become more powerful. During the signing of the peace treaty between the Three Factions, Issei fought him when Vali went against everyone and formed a team of his own in the Khaos Brigade. In an attempt to bait him into fighting harder, Vali not only insulted Issei's lineage but also threatened to kill off his parents. This enraged Issei, causing him to engage Vali in his Balance Breaker mode, which was only achieved temporarily thanks to Azazel's bracelet. Regardless, Issei, seemingly, was able to defend against Vali either due to latter holding back, or due to his underestimation of Issei. However, the fight remained inconclusive since Vali was interrupted and was teleported away just before he could enter Juggernaut Drive, by Bikou. Later on, however, the two of them would join forces in order to defeat Loki, and after that, begin cooperating with each other on multiple occasions. Later into the series, the two of them have started to become friends; although they are still in a heated rivalry. They even promised to fight each other someday and continue to grow stronger until then.
Unlike the rest of the Khaos Brigade, Vali did not make use of Ophis. When he came to believe that Cao Cao and the rest of the Hero Faction might attempt something against her, he sent her secretly to the Hyoudou Residence to keep her safe. He was also Ophis' talking partner during her time as the leader of the Khaos Brigade.
After being discarded by his father (his mother being the only one who loved him, but could do nothing to protect Vali from his father's abuse), who called him a monster, it was Azazel who took Vali into his fold, becoming a surrogate father to him in the process out of sympathy. Despite this, Vali betrayed Azazel during the meeting between the Three Factions by becoming a member of the Khaos Brigade in order to fufil his desire to seek out battles with strong enemies. He has shown strong loyalty and respect towards Azazel, willingly dealing with Kokabiel on the latter's instructions. Vali and Azazel have a father-son bond and Vali himself became incredibly enraged when he saw Azazel being badly injured by Cao Cao. Azazel is probably the only person who understands Vali's deepest thoughts and emotions and despite Vali being renowned for his battle maniac personality, Azazel correctly figured out what Vali truly desired is not power, but a happy family like Issei's. The two have also been shown to co-operate well in battles. In Volume 21, it was shown that Azazel is the ideal father Vali has desired, and Vali himself stated that meeting Azazel is one of the biggest blessings he ever had. When Azazel leaves for the Isolation Barrier Field, Vali desperately begs Azazel not to leave him, reminiscing the time he spent together with Azazel since his childhood days.
Vali considers Bikou as both a partner and a close friend. They are usually seen hanging out together because of their close friendship.
Arthur and Vali have great respect for each other as both a leader and as a friend, and are willing to fight together.
Vali has great respect for Le Fay due to her superlative skills in the art of magic.
Kuroka cares and respects Vali, and sees him as an important friend. As a comrade of his, Vali was shown to become enraged when Cao Cao endangered her, even more so that he used Vali's own power to do it.
Vali and Fenrir both enjoy fighting as both of them seek stronger and more powerful people to fight.
Vali had an antagonistic relationship with Cao Cao. Vali constantly meddled with Cao Cao's schemes, such as sending Le Fay to aid Issei's group when Cao Cao ambushed them and later sending Ophis away to a safe place in an attempt to keep her away from Cao Cao. During their fight, Vali became enraged when Cao Cao injured Azazel and then attacked him recklessly, Cao Cao further enraged him by using an attack to injure one of his own teammates. To date, Cao Cao is the only person who made Vali enraged enough to use his Juggernaut Drive out of anger instead of necessity.
Initially, it was said that Vali and Tobio hate one another, but it is was revealed in Volume 19 that Vali seems to share an older brother-younger brother type of relationship with Tobio. In the past, Tobio and Vali lived together, so they know each other quite well. According to Tobio, Vali is very clingy, comparing him to a troublesome little brother, so he avoids seeing him.
Vali has shown to care about Lavinia and sees her like a older sister. Vali is also fearful of her, as seen upon reuniting with her in Volume 21 and tried to run away from her. Lavinia gave a gentle scolding to Vali for acting on his own to find Rizevim and hugged him. She also likes to tease Vali, calling him "Va-kun".
Shalba hates Vali for being a half human-devil hybrid due to his pure blooded views, Vali himself also seems to believe Shalba's ideals of world domination are delusional and naive. They have a purely antagonistic relationship as Shalba called himself a "true Satan" while Vali stated that he didn't want to hear Shalba who borrows power from someone else than himself (Ophis) a Satan.
Vali's grandfather, who Vali utterly despises for his part in the bad treatment Vali got from his father. Vali's hatred towards his grandfather is so immense that in Volume 15, Azazel noted that Rizevim was the only person who was capable of provoking tremendous anger in his own grandson, and in Volume 16, Issei himself noted that he has never seen Vali openly express so much anger which strongly contradicted his calm and collected nature, when Vali first reunited with Rizevim for the first time since he was a boy. Vali also stated that Rizevim was the person he wanted to kill the most when they reunite and considered him a scum who does not deserve to carry the Lucifer name. Rizevim himself was fully aware of the immense pain Vali suffered as a boy due to the advise he gave his own son; Vali's father years before, and found sadistic amusement in his grandson's extreme anger towards himself even addressing Vali affectionately as Vali-Kun. He also particularly enjoyed toying around with his grandson in combat. When Rizevim was fatally injured by Issei in Volume 20, Vali ruthlessly hunted Rizevim down and was shown to be absolutely merciless, completely ignoring his grandfather pleas to spare his life. When Rizevim was brutally killed by Fafnir, Vali felt completely no sorrow towards his demise.
Similar to the relationship between Ddraig and Issei, Albion seem gets along with Vali very well; Albion gives advice to Vali for fights and dailylife, while Vali has shown to care deeply for Albion, feeling troubled when Albion fell into depression and tried to find a method to make Albion feel better.
The two of them have a very antagonistic to each other, since their first meeting. But both of them shared a deep respect and honour to each other, as Azi Dahaka claims he is the strongest of all he have fought, he shows it when he apologize to Vali, for creating a lowly technique to him. After their battle Azi Dahaka said that he will return one day and will fight him again.
As a child, Vali was brutally abused by his extremely arrogant Devil father out of intense jealousy towards Vali's ownership of a Longinus supplemented with the inherited demonic powers of Lucifer, that would eventually surpass his own power. His father was completely cruel to the point, that he even ruthlessly abused Vali's mother simply for showing Vali the slightest kindness, thus Vali held immense hatred towards his father to the point Vali even swore to commit patricide for revenge and was perfectly content to learn that his father had died without a single shred of care.
Vali's mother was a very compassionate woman who did everything she could to protect Vali from his father's cruelty despite being completely powerless before his great power as a descendant of Lucifer. Being extremely sorrowful and sympathetic with her son's plight, Vali's mother would secretly bandage Vali's wounds and cooked simple pasta to feed him despite the serious consequence of being subjected to cruel abuse by his father. Vali is extremely protective of his mother and cares greatly for her well being. When he found out that she had gained a happy family after remarrying a Human husband and birthing two children, Vali was determined to protect his mother and half siblings at all costs. It was their safety and protection that drove Vali to gain the willpower to defeat Aži Dahāka in an brutal death match.