In this other world, Ichigo could be paired with a local mage. This mage could initially be distrustful of Ichigo but as they go through adventures together, they start to develop a deep connection. The mage could teach Ichigo about the world's magic, and Ichigo could teach the mage about his spiritual powers.
Rukia could be a great character to pair with Ichigo. Since they have a strong bond in the original series, in the fanfiction, she could follow him into the other world or be summoned there later. Their combined power and friendship would make for an interesting dynamic as they face new challenges.
Uryu could also be an interesting character to include. He might end up in the other world separately from Ichigo and they could reunite. Their rivalry - turned - friendship could add a layer of complexity to the story, especially when they have to work together against new enemies in the unfamiliar world.
Rukia could be a great character to pair with Ichigo in a different world crossover. She has her own set of powers and a calm, intelligent mind. In a strange new world, she could help Ichigo analyze new situations and come up with strategies. Their bond as comrades from the Soul Society would be interesting to explore in a different setting.
One popular character paired with Ichigo is Naruto. Their different power sets and personalities make for an interesting combination. Naruto's positive and determined attitude could contrast with Ichigo's sometimes brooding nature. Another is Luffy from 'One Piece'. Luffy's carefree and adventurous spirit next to Ichigo's more serious approach to protecting his friends can create some great stories.
Obviously, Ichigo and Dark Ichigo are the central characters. Ichigo, with his complex personality and powers, is always a key figure. Dark Ichigo, being his inner Hollow, brings a lot of drama and conflict. The OC also becomes popular depending on how well - written they are. If the OC has unique powers or a really interesting backstory, they can gain a following among fans of the fanfiction.
Uryu could also be a main character. He might be initially skeptical of Ichigo's transformation into a dragon god but then come to respect and even rely on his new powers in battles against common enemies. His Quincy abilities could contrast with Ichigo's dragon god powers, creating interesting interactions between them.
Rukia could be a character. She might come to Ichigo's rescue when she hears about his situation with the tentacles. She could use her own powers to freeze or cut through the tentacles. Another potential character is Uryu. He could use his Quincy skills to disrupt the energy of the tentacles. And there's also Orihime, who might use her shield - like abilities to protect Ichigo from the tentacles.
To create believable characters, study the original Ichigo's personality traits. He's brave, determined, and has a strong sense of justice. For fem Ichigo, you can keep some of those core traits but also add some feminine touches. For example, she might be more in touch with her emotions but still be as fierce in battle as Ichigo.
One interesting character to crossover with Ichigo is Light Yagami from Death Note. The clash between Ichigo, who is a protector, and Light, who is a morally ambiguous character with the power to kill, would be very engaging. Saitama from One - Punch Man could also be a great choice. Saitama's overpowered nature and Ichigo's journey to become stronger would make for an interesting story. And what about Alucard from Hellsing? His vampire powers and Ichigo's powers related to the afterlife would create a really dark and exciting crossover.
His friends Orihime and Chad would probably be main characters. Orihime could be very motherly towards baby Ichigo, always making sure he's comfortable. Chad would be the strong protector, making sure no harm comes to the baby.
In the world of Harry Potter, a crossover with Harry could be interesting. Ichigo's immortality would put him in a unique position in the wizarding world. He could bring his combat skills to Hogwarts and perhaps even help in the fight against Voldemort, while also learning about magic and how it differs from his own powers.
Ichigo would likely be a bit brash at first. He's used to dealing with things on his own terms in the world of 'Bleach'. Izuku, on the other hand, would be very respectful and inquisitive. He'd probably ask a lot of questions about Ichigo's powers. Ichigo might be a bit impatient with all the questions but would soon realize that Izuku is genuinely interested. They'd start to bond over their shared desire to protect others.