just want to know about celicas attributes,if the willpower is at 100,should she be able to resist the demoness and nel's possesion,i want to make some of those decisions myself instead of them being done for her?
The essence of the problem is not always in the attributes. There is also a plot, which is still quite straightforward, in many moments.
Therefore, you are actually obliged to be friends with Nel, in all senses.
And in order to defeat a character in a duel, it is important for you to take into account the attributes. Especially yes, willpower, speed, arcana. And, it is often important that Celica is not liberated. The value of the lower scale is less than 30.
Much depends on the specific opponent, because they are tied to the elements and to the level of experience. And some other parameters. Studying the weaknesses of the opponent is called preparation, which Celica sometimes talks about.
First of all, it's an RPG. So it's important to think, but the many beautiful girls in the game distract from that :-)