When they first met (not counting the Have Time, Will Travel arc), Harribel was polite and courteous to Ben, and remarked that he had good manners when he managed to keep himself from staring at her. When Ben chose to be one of her Fraccion, Harribel was surprised, but nonetheless did not protest.
Ben slowly began to gain Harribel's trust by saving her Fraccion from Nnoitra Jiruga; this was particularly important in Harribel's case, since she was one of the few Espada who cared about their Fraccion. When Ben used Way Big to give Nnoitra a brutal beating in retaliation for attacking Apacci, Harribel was touched.
As time passed, Harribel's feelings towards Ben blossomed into love, going as far as to betray Aizen in order to help Ben. Her love for Ben greatly increased after she recovered her memories at the end of the Have Time, Will Travel arc, and soon after, they began a relationship, sharing their first kiss.
Nelliel Tu OdelschwanckEdit
When they first met, Ben thought Nel was adorable, and later on, he developed a sort of older brother complex towards her, being very protective of the young-looking Arrancar. Nel, in turn, claimed that she loved Ben, to which Ben simply dismissed as a childish crush. When Nel assumed her true form, Nelliel, Ben was visibly shocked, and quickly became embarrassed when he realized that Nelliel's feelings for him were more than a childish crush.
Over time, he began to return her feelings.
Apacci initially did not trust Ben, and threatened violence should he give an incorrect reason for joining Harribel's Fraccion. Over time, though, she began to trust and eventually love Ben for his personality.
At first, of the Tres Bestias, Ben was more comfortable around Sung-Sun, who was more polite and accepting to the young hero before Apacci and Mila-Rose. She was even the first of the three to go on a date with Ben.
Franceska Mila RoseEdit
At first, Ben was a little afraid of Mila Rose, due to her tough attitude and her along with Apacci threatening to kill him if he disappointed Harribel. She began to warm up to him as time went by, and this eventually developed into love. Realizing that Harribel had also fallen in love with Ben, Mila Rose planned to give up on him in the hopes of helping her mistress win his affections, but when it became clear that they could "share" him, she was delighted and openly flirted with him. During their trip to Altrox, Mila Rose stepped up her game by flaunting her naked body in front of Ben and eventually "marking" him as her own by biting him. Ben showed his trust in her afterwards by giving her the blade the Yautjas gifted him in respect of defeating their fellow hunter.
When Ben was asked to choose which Espada he would serve under, even though he said that Harribel had a less off-putting presence, he mentioned that would have chosen Starrk is he wasn't so lazy. Later, in the battle in Karakura Town, Ben did everything he could to convince Starrk to help him fight Aizen, and was angered to find out how Aizen manipulated both of them with their loneliness, and claimed he would be a true friend, one who would actually care about their well-being, and when Lilynette asked what he would do about the Shinigami should they attack both of them, Starrk joined him after learning that Ben was ready to fight them if need be. The two are now good friends, and comically, Starrk often seeks relationship advise from Ben.
Even though Lilynette was hostile towards Ben, when the former believed the latter was a traitor, Ben refused to give up on her and manages to convince Lilynette and her other half Starrk that he was their true friend. Over time, Ben and Lilynette developed and good Brother-Sister relationship.
Ulquiorra's emotionless behavior disturbed Ben when they first met. However, ever since Ulquiorra moved into Bellwood, Ben trusts Ulquiorra deeply.
Even though Ben is not comfortable with Yoruichi's flirting habits, he still sees the Goddess of Flash as a friend and ally.
When Ben first came to Hueco Mundo, Tosen was one of the only people he felt comfortable around, and saw him as a good friend. When the came came for the Winter War, Ben did everything he could to make the former 9th Squad captain realize following Aizen was a mistake.
Jushiro is one of the few captains who was polite to Ben. As such, Ben holds him in high regard.
Ichigo and Ben have a good relation with each other, fighting together effectively. When Ichigo was killed by Ulquiorra, Ben was both horrified and enraged, turning into Ghostfreak and savagely attacked the Cuarta Espada in his true form.
Ben first met Orihime while he served under Aizen, and protected her from Tsubaki while in his Nanomech form and revealed the Ultimatrix and did what he could to make her feel better, and when Ulquiorra says that she would join Aizen, Ben declares she would not, citing that he had been with them longer, showing that he trusts her. Their relationship is best described not as a romantic relationship, but rather that between a brother and sister.
Ben first met Uryu (along with Renji) when he and Nelliel arrived to battle against Szayel. The two instantly became allies and later good friends. They have even shown to fight well together as seen when they; along with Nelliel, fought against Nnoitra, Szayel and Tersa in a Three-way battle.
Gwen Tennyson Edit
When he and Gwen were younger, they did not like each other very much, and they frequently argued, but they genuinely cared about each other. In the present day, he and Gwen are each other's favorite cousins, and when he met up with Gwen and Kevin after fighting Yammy, he and Gwen had a tearful reunion.
Kevin Levin Edit
When Kevin and Ben were younger, the two hated each other greatly, with Ben seeing Kevin as a monster, while Kevin blamed Ben for his mutation. In the present day, Kevin is one of Ben's trusted friends, and while the two do argue from time to time, and as of recent times Kevin does mock Ben on his harem, they still care about each other.
Originally, Ben was just another one of Aizen's soldiers, loyal to him after hearing about the "oppression" of Arrancar under Soul Society, and while he served under him and followed his orders, Aizen only saw him as yet another tool to use against the Shinigami. Over time, though, Ben's morals started making him see that Aizen, while he did not, at the time, see him as a bad person, did not particularly care for any of his soldiers, as seen with his brutal punishments. He was pushed over the edge after Tia revealed the truth about Aizen's plans to use the Hogyoku, eventually betraying Aizen, and the more he heard about his actions, the more Ben began to hate the psychopathic Shinigami, especially after learning that he was the one responsible for giving the Vizards their powers. Ben was especially enraged and anguished when he nearly killed Nelliel, Tia, and Starrk, and his rage was so much that he was willing to erase Aizen from existence, but when he realized doing so would make him no better than him, he decided to punish the criminal for his actions by stripping him of his powers, while still allowing him to live at the same time.
At first Ben saw Nnoitra as a dangerous being, he personally gave the fifth Espada a severe beating twice; for hurting Apacci and for hurting Nelliel. However, the more Ben fought the fifth Espada, the sooner he saw him as no more than a pathetic nuisance. When he fights him a third time, Ben outright calls him a sore loser and refuses to kill him, even despite Nnoitra's pleas to do so.
Szayel Aporro GranzEdit
Loly hates Ben, whom she blames for Aizen's death. Ben, in turn, seems to pity Loly, though this doesn't stop him from being rather merciless towards her in battle.
Ben and Toshiro share an uneasy relationship. Toshiro clearly bears a grudge against Ben for humiliating him in battle, whereas Ben does not seem to show much respect toward the young captain, much to the latter's annoyance.
Ben and Sui-Feng are on neutral terms; for one thing, Ben is not fond of Sui-Feng due to the latter's racism about the Arrancar, while Sui-Feng loathes Ben for "stealing" Yourichi from her.
Due to Mayuri being a mad scientist who wants to study the Ultimatrix, Ben is, quite rightly, unsettled by him and dislikes being around him. Another possible reason is due to Mayuri's clown-like appearance, as Ben used to be afraid of clowns when he was 10 years old.
Genryusai Shigekuni YamamotoEdit
Ben detests Aizen, and the feeling is quite mutual. He regards Aizen as a coward with an overly inflated ego.
Mayuri, being a mad scientist, wishes to study Ben very badly. Ben is, quite understandably, reluctant to be around Mayuri. He is also disgusted by Mayuri's treatment of Nemu.
Genryusai Shigekuni YamamotoEdit
Ben has a low opinion of Nimaiya, regarding him as overly obnoxious and time-wasting. He was particularly hostile to Nimaiya's attempt to force Ichigo to go on a "self-discovery trip" instead of "throwing him a bone", which culminated in Ben, with the help of Paradox and Azmuth, blackmailing Nimaiya into unlocking Ichigo's true powers without such a "journey". Nimaiya has held a grudge against Ben ever since.