Disclaimer: First Chapter
Time to Answer Some Questions, and Misconceptions.

1. When will Naruto's chakra stop hurting Asia?
Answer: Never, the reason it hurts her is because her body just flat out is not compatible with it. Naruto was born long after the time of the Sage of Six Paths giving people chakra, so his body developed Tenketsu and a Chakra Network in order to better use chakra.
When Naruto uses chakra in Asia's body, the chakra explodes out of her body where the Tenketsu points would be, which damages her.
Naruto's chakra is compatible with her SOUL, but it is NOT compatible with her BODY.
Naruto has not realized this, but he does understand that if he trains her body enough, he won't have to use his chakra and hurt her body as often.

2. Why is the chakra Naruto has access to so limited?
Answer: Because he isn't really Naruto, he is a small portion of Naruto that gained a soul, connected to the main body. The maximum amount of chakra he has access to is about equal to the amount of chakra that was inside of the severed hand that Asia found.
Since he IS still connected to the main body in another dimension, so he still gets chakra from the Main Naruto in his Home Dimension.
For the amount of chakra he gets to increase, the connection between himself and himself would need to get stronger.

3. GIVE NARUTO HIS OWN BODY!
Answer: No.
Not only no, but HELL NO! If I were to do that, then it would just become another "Naruto in DxD charming girls" story, without anything really super special. I started writing this story with the idea of "A boy and girl who share a body fall in love", and I want to write the trials and difficulties that come with that idea. This is a concept that has not really been done, and I want to explore.
Naruto getting a body of his own goes against the concept of the story.

4. When will people realize Asia is sharing her body with Naruto?
Answer: When somebody actually tries to ask Asia what is happening with her, since right now everyone just assumes she has a split personality. The only person who knows she can communicate, right now, with her other personality is Sirzechs, and the only other people who figured out something is 'off' about her is Xenovia and Koneko.
Also, there is a secret condition that will let others see Naruto, but I'm keeping it a secret from everyone not on my discord, as a Discord Perk.

Warrior (Naruto)
White Mage (Asia)
Naruto using the body (Warrior White Mage)
Asia using the body (White Mage Warrior)

Hope this cleared some stuff up.