Hi, I hope everything is alright with you. I hope you can continue with your story cause I just love it. I have a few ideas for the other arcs if you would use them.
For Tenrou island you could have that the celestial king gives Lucy a special necklace to wear for the s class test. The necklace would transfer their souls to another world while their bodies stay within the fairy sphere. They would stay in the world for 4 or 3 years for them but 7 in their original world to train. This way they have more time to train and learn new things, especially for Lucy. The whole celestial mage concept should have been very powerful but it's not for some reason. You could give her new spells with her spirits, use magic that has to do with the plants or what I really hoped for Lucy is to merge with her celestial keys. I know Star Dress is her using some of the spirit's power but I think it would be more better or powerful if she could use their full potential. Like the key is limiting their powers while merging with them allows her to use their full power.
For example: Leo - could be a werelion with a collar that has the symbol of leo and she can change form a werelion to a lioness but this has it ups and downs. In this form she would have a tough hide like the Nemean lion and claws that could cut magic. This in turn would give her great strength and defense but have lower stamina.
Something like that with either some or all if you want with the others.
Natsu meets Zeref and tells him to leave while Zeref sense something different about Natsu. As for Grimore hearts that is up to you.
I really hope that this can help you in any way and for you to continue your story. If you like my ideas and want me to help you get any ideas for the upcoming arcs I would gladly help.
