Hestia has feelings for Bell but he doesn't return them due to the thought of respecting Gods and Goddesses. She is also possessive and often tries to ward off other girls, especially Ais Wallenstein, from Bell.
As of volume 8, Bell has decided to accept Hestia's feelings instead of just respecting her, however it is unknown whether he feels anything for her in return.
Bell and Lili have a very friendly relationship. Bell has gone to great lengths to save Lili, the first time in the Dungeon and the second time from Finn after she supposedly accepted his proposal. Although he likes Lili as a friend, he is oblivious to her feelings.
Due to her personality, Mikoto felt bad for pass parading Bell and his companions, and has supported him since then, first as a member of the Takemikazuchi Familia, and later as a member of the Hestia Familia after converting to assist him in the War Game.
Bell rescued Haruhime despite her thinking that as a prostitute she shouldn't be saved. He proved to her that a hero will save anyone regardless of the circumstances. The two have a very friendly relationship with Bell trying to help Haruhime whenever he can and Haruhime in turn tries to do her best. She is in love with Bell.
Bell first met Ais when she saved him from a minotaur. Because of that, Bell fell in love with her and gained the skill Liaris Freese. Ever since then Bell and Ais have had a friendly relationship with Ais assisting Bell whenever he needed help, such as before the battle with the Minotaur and before the War Game with the Apollo Familia.
Bell and Ais have a positive relationship as she constantly helps him and she even accepted his invitation to dance even though it was her first time. During the Xenos arc, Ais and Bell did fight but Bell was able to end things on a positive note with him asking Ais to train him again.
Tiona has a friendly relationship with Bell. She's been interested in him ever since he defeated the Minotaur. Tiona calls him Argonaut-kun and was even willing to help him train with Ais. She also excitedly told Gareth Landrock about how cool Bell was.
Bell met Syr on his way to the dungeon when Syr called him over to give him a magic stone he had supposedly dropped. Ever since then she has made lunch for him almost every day and has been worried about his safety in the dungeon. Bell acquired his magic when Syr loaned a Grimoire to him. After she witnesses Bell defeat a Silverback, she confessed to him that she fell in love with him after witnessing that feat though Bell assumed she was just teasing him.
Ryuu and Bell have a positive relationship and are good friends, with Ryuu even letting Bell touch her skin despite her elf heritage. She has shown romantic feelings for him but tries to keep them hidden in respect for Syr, who she thinks will marry Bell.
Eina has been Bell's dungeon adviser since he registered to become an adventurer. Due to her past, she takes their relationship as adviser and adventurer seriously, warning him to not go on an adventurer and teaching him about the various dangers of the dungeon. She originally thought of him as a younger brother, but after the events of volume 11, she begins to develop personal feelings for him.
Freya has taken an interest in Bell, due to his transparent soul, ever since he passed through her gaze. She is obsessed with him and takes advantage of certain incidents in order to unleash his full potential.
Bell first met Mord when the drunken adventurer offered him to join his party in exchange for sharing Lili, Syr, and Ryuu with him. Before Bell could do something, however, Ryuu and the other waitresses of the Hostess of Fertility dealt with him and his companions.
Afterwards, while Bell was also on the 18th floor, Mord expressed annoyance and anger for Bell's quick rise to Level 2 and subsequent fame. With some help from Hermes, Mord kidnapped Hestia and forced Bell into a duel, in which he began to beat up the boy. The fight was stopped not long after by a rescued Hestia. Despite this, Bell did not hold a grudge against Mord. During the Black Goliath's appearance on the 18th floor, Bell rescued Mord from a monster.
After Bell defeated the Black Goliath, Mord gained a sense of respect for him. He is now openly friendly with Bell and one of his staunchest supporters. Just before the War Game between the Hestia and Apollo Familias, Mord bet 100,000 valis on the former with no hesitation. Mord even took Bell out to gamble after his victory. When Bell's reputation was destroyed following the Xenos incident on the surface, Mord became angry and defended Bell when others mocked him. During Bell's fight with Asterius, Mord was the first to give him his vocal support.
Bell first encountered Aisha in the Entertainment District after getting lost looking for Mikoto. He found her extremely attractive, but was unnerved when she showed interest in him. After finding out who he was, Aisha's interest grew much stronger. She was one of the many prostitutes to chase after him throughout the district.
After Bell met Haruhime and learned about Ishtar's plot to sacrifice her, Aisha intervened. She told him and Mikoto how she once tried to protect Haruhime from being sacrificed before, but was severely punished. When asked if he would try to save Haruhime, Bell was unable to answer, fearing retaliation from the Ishtar Familia. Aisha mocked him for his indecision and said he didn't have it in him to give up everything to save someone and left with Haruhime.
Once Bell and Mikoto resolved to save Haruhime and destroyed the Killing Stone necessary for the sacrifice, he again confronted Aisha. He stated his resolve to save the girl, much to Aisha's approval, but the Amazoness said she couldn't just stand by and let him do so due to her Familia bond. Even so, Bell let Haruhime's level boost magic wear out before their duel. During their fight, Aisha expressed her excitement and joy in fighting a real man. Despite losing to him from a point-blank Firebolt, Aisha smiled as she flew through the air.
Afterwards, Bell promised Aisha that he would protect Haruhime and the two now have a friendly relationship. Bell holds faith in her strength and experience in the Dungeon, having no objections when she has traveled with him. However, he still gets flustered around her due to her raw sex appeal, especially whenever she expresses her desire to sleep with him.
Bell and Hermes used to have a friendly relationship, with Bell holding a lot of trust in the God. Hermes came to Bell's assistance when he was trapped in the Dungeon, helped to give Bell an opportunity to dance with Ais, and gave him and Mikoto advice on how to free Haruhime from her life as prostitute. Bell even noted that Hermes was the best oral tactician he had ever met.
Likewise, Hermes sees a lot of potential in Bell. After the battle with the Black Goliath on the 18th floor, Hermes was filled with excitement due to Bell's performance and became one of his fans. However, Hermes has also put the boy in harm's way to see his potential. He helped Mord kidnap Hestia in order to teach Bell about the darker side of humanity and for the fun of it. He told Ishtar about Freya's infatuation with the boy, which caused the Hestia Familia to be ambushed by the Ishtar Familia. Bell remains unaware of these actions, and doesn't know that Hermes was asked by his grandfather to check up on him.
Their relationship became strained after the Xenos incident of the surface. Due to defending Wiene from other adventurers, Bell's reputation plummeted. Worrying for Bell and believing that coexisting with monsters is nonsense, Hermes set up a plan to trap the Xenos in a dead end tunnel, with him alone knowing the way to the Dungeon. In exchange for that information, he asked that some of the monsters rampage on the surface so that Bell could kill them and have his reputation restored. He asked one volunteer, Gros, to attack Eina so that Bell would have no choice but to do so. To his shock, Bell chose to believe in the dream of the Xenos and risked death rather than kill Gros.
Afterwards, Hermes told the truth to Bell about his actions. Bell could not decide if he hated the God due to his help in the past, but Bell could not forgive him either. Hermes took it in stride and said he would continue to meddle in his life, telling Bell that he was his fan.
Bell's adopted grandfather and his only family member growing up. Zeus nurtured Bell's desire to one day travel to Orario and be a hero, as well as his desire to have a chance encounter with a girl. Bell loved Zeus dearly, and he was filled with a deep sense of loneliness upon hearing of his grandfather's supposed death. Whenever Bell is unsure of himself or what to do, he thinks back to a piece of advice Zeus once told him or would imagine what he would say now if he were there, giving Bell the resolve and strength to move forward.
As of yet, Bell does not know that his grandfather is still alive, nor does he know that he is actually a God.
Wiene is the first Xenos that Bell befriended and the one he is closest to. Upon their first encounter, Bell was stunned upon her more human appearance and the fact she wasn't showing behavior typical of a monster. He tried to pretend he didn't see her at first, but rescued her when he saw that even other monsters attacked her. After discovering that she could speak and smile just like people, he decided to protect her.
Bell cares a great deal about Wiene, teaching her some things about the surface world and being gentle with her, and was able to use Argonaut while moving for the first time due to her being in danger. In turn, Wiene trusts Bell above everyone else, even refusing to leave his side for a time. When Bell and the rest of the Hestia Familia were tasked with bringing Wiene to the Xenos hidden village, he was saddened that he had to leave her behind, promising her that they would see each other again.
When Lyd told him that Wiene had been captured by hunters, he became determined to help find her, despite the Lizardman's objections. When her Vouivre's Tear was ripped out and she went on a rampage on the surface, Bell protected her from other adventurers, though it caused his reputation to plummet. When Wiene's magic stone was cracked, she told Bell that she was happy he was there to save her and that she loved him before turning to ash. Bell was heartbroken and was about to cry out in grief if not for her resurrection by Fels.
Even with his reputation in shambles, Bell still wanted to help Wiene and the other Xenos that were trapped on the surface make their way back to the dungeon. Bell even fought against Ais to protect her, desperately trying to convince the Sword Princess that Wiene was not like other monsters. Before parting ways, Bell promised her that he would make a world where they could live together, using a pinkie promise at Haruhime's suggestion.
Bell first encountered Lyd when he and the Hestia Familia were taking Wiene to the Xenos hidden village and were attacked by him and other monsters. After delivering an Argonaut-charged punch to the cheek to the Lizardman, Bell was shocked when he suddenly started to laugh and speak fluently. Lyd happily greeted Bell and apologized to him, revealing they had been testing them to make sure he and the others would protect Wiene. Lyd even gave Bell a nickname and offered him to shake hands. Though Bell was afraid of his appearance and felt like refusing, he remembered his encounter with Wiene and worked up the courage to shake his hand, much to Lyd's delight.
Despite finding his appearance intimidating, Bell thought Lyd to be quite personable. He felt that his constant laughter helped to put him at ease, and he was able to recognize his facial expressions after some time. When it came time for the Hestia Familia to leave, Lyd told Bell to not hold back on killing monsters for the Xenos's sake, as he didn't want Bell to die. It was his words that helped Bell keep on doing so despite his hesitation.
After Wiene and Fear had been captured and the Xenos attacked Rivira, Lyd told Bell what had happened and expressed his rage. Though Bell was slightly scared of his monstrous demeanor, he sympathized with what he was feeling, noting that humans felt the same things that the Xenos were. While fighting Dix Perdix, Bell stated his belief that the Xenos were worthy of being saved, giving Lyd the strength to fight Dix's curse and save Bell, apologizing and thanking him for his words.
Asterius is the Xenos reincarnation of the Minotaur Bell defeated on the ninth floor. He was reborn through his extremely strong desire to have a rematch with Bell. After losing to Asterius in a close battle, Bell resolved to grow even stronger. He views Asterius as his rival and desires to be strong enough so that he can one day settle the score.
Bell's fight with Asterius also caused him to mature, as he became more calm and level-headed upon ascending to Level 4. He decided to study his magic and skills instead of just using them, trying to discover any new techniques that he could use against Asterius, like Argo Vesta.