Sayantan2971996
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Fairy Tail should be the best choice as it is of similar power levels and also there he can practice his gravity related powers better. Bleach should be a little higher level than One piece. DXD will be good choice to go but mc will not learn or hope to obtain there other than evil pieces for his crew. Demon Slayer is too low levelled. Best would be to go to where he will receive insight about gravity and its uses. His application about gravity as a fundamental force and pressure is very low.
I choose option 2. Bell is a good choice but it is already done and frankly if not for his looks and his growing skill, Bell does not have much to offer. As we know that Bell's mother was pure but not strong. So a son of Zald and Alfia who gave their lives for Orario twice would be a better choice and we can mix their bloodlines and skills and make a killer main character. Plus we can have a good backstory for it.