You're welcome!
Yes, I noticed that all of the bonuses you select after beating the game can only be accessed after you reach Asura city. In which case there's only 6 more fights left in the entire game + whatever extra devils you've yet to defeat. So early bonuses that help before you reach Asura city would help a lot. Even something like the upgraded ring shop being accessible in one of the villages would be a big help.
Optionally, you could add some bonus fights before the player faces the Asura King's men. There could be an event where you hunt new borns just like what happened to you at the start of the game. Or maybe some extra hunters that aren't required to progress? Just some guys who are standing around and you only need 8 wins to reach the city. Besides the new enemies, which you'd need multiple playthroughs to fight, you don't get many opportunities to use all the new equipment, spells and weapons you've gotten. So basically once you get strong in this game, it ends.
I'd say you should show a lot of changes on the second playthrough so that the player really feels a difference. That's where most people will either quit or keep playing. When you start a new game +, you don't get to keep anything and it feels daunting to try again, starting from nothing.
Perhaps you could allow the player to select a unique special power when they start their second play through? It takes some of the sting out of going from beating the Asura king to being a weakling again. All the other hunters have unique abilities and the player is the only one who doesn't. It would make sense if you could do something special like everyone else.