Among the main characters besides Rimuru are Gobta. He is a goblin who is rather comical at times but also shows growth throughout the story. Then there is Diablo, a very powerful demon who becomes Rimuru's subordinate. His power and knowledge contribute to Rimuru's rise in the world of the novel. There are also other characters like Milim, a dragonoid with a child - like personality who has her own impact on the overall plot.
There's Veldora. He's a powerful dragon sealed within Rimuru's stomach at first. His presence has a great impact on Rimuru's growth and the story. Then there's Shion, a strong ogre who becomes one of Rimuru's loyal followers. She's known for her combat abilities. Also, Benimaru, a kijin, is an important character. He plays a key role in the development of Tempest.
Rimuru is very strong in the manga. He starts off with some unique abilities and keeps getting stronger through different events and encounters. His strength is not just physical but also in his strategic thinking and leadership skills.
He'd probably be shocked by the different power systems. Naruto is used to chakra and jutsus, while Bleach has spiritual energy and zanpakutos. So it would be a big change for him to read about.
Rukia would probably be both amazed and a bit worried. Amazed at the new power Ichigo has, but worried about how it might change him. Chad would see it as a natural progression of Ichigo's power and be supportive. Orihime might be a bit scared at first, but then she would see the good in Ichigo's new form and try to encourage him.
Chad would be a very protective and gentle presence. He would be like an uncle to the baby, always ready to pick the baby up and play with it. His calm and strong nature would make the baby feel safe.
Some of them could be entertained. For those who are more open - minded, like Yoruichi, she might find it fun to see the different interpretations of their world and the characters in it. However, others, like Byakuya, might be more critical and think that the fanfiction distorts the original values and stories of the Soul Society.
The Soul Reapers in the Soul Society would see Ichigo as a major threat. They would likely mobilize their forces to either capture or eliminate him. Captains like Byakuya would be disappointed as he had come to respect Ichigo to some extent, and now would see him as a traitor.
Rukia would probably be one of the first to be both shocked and amused. She might tease Ichigo a bit at first but then quickly get serious about helping him. Chad would be very accepting and offer his protection as usual. Uryu might be a bit more skeptical at first, thinking it's some kind of new Hollow trick. Orihime would be very empathetic and try to make Ichigo feel comfortable in his new form, maybe even offer to make some new clothes for him to fit his new body.