Alright, time to get down to business.
First things first. On the surface, Endless Nine is conceptual immunity to magic from virtually any beings of[a comparable or lower level of existence (
https://imgur.com/a/q8BbfaZ) While this alone is impressive, it should be noted that a consequence of the nature of magic in 07th is that it encompasses existence and nonexistence on a conceptual level, fate, the laws that govern reality, what is possible and what is not, etc.
As a result of this, truths in Umineko are far more than just conceptual attacks that target the opponent. Even while restricted by the rules of a gameboard and even when used by a piece like the Battler in this
battle (NPI), they are capable of altering the structure of reality as to make the opponent's victory impossible. Furthermore, attacks of that nature are well within the paygrade of Endless Nine and will likely be easily negged. While Nanashi can resist conceptual attacks, so can every decent opponent in Umineko; a degree of resistance doesn't imply that he'd be able to no sell a barrage of truths especially considering the relative scale of their powers (9-D vs at least 10-D). Nanashi's dura neg only works on comparable enemies, a minimum full dimensional level between the two means that ain't happening; Battler can one-shot Nanashi but the reverse isn't true.
Battler has been shown to be capable of quickly adapting to a diverse array of strategies and, again (
https://imgur.com/a/yIMnJOQ)
using his abilities within the restrictions of a gameboard in which the rules were not set by him.
NOTE: I'm not finished but I have to get back up to the desk at work, there's nothing going on so I'll likely be able to finish it up there but let it be known that I haven't typed out
extremely important parts of my argument yet. This is probably about 1/3 of it cuz I hadda rush.
Now, how is Battler going to deal with Observation? Given the difference in the scale of their abilities, it's likely that he can simply neg it but even rejecting that idea, truth is a natural counter and denying the 'answer to which there is no answer' is something that multiple manifestations of Battler constantly do (including his piece self) over the course of the first half of Umineko. What about High-Godly Regen? Battler doesn't need to conventionally erase Nanashi and will likely quickly realize it isn't a viable option after the opening stages of their battle. He can deny the
possibility of Nanashi's existence and enforce his truth with power on a much higher scale than the latter has encountered (i.e.: affecting the laws of whichever reality it is they're fighting in).
EDIT2: Sorry, I gotta do this again guys but I don't have time to finish my points here as I gotta get off the computer in a few min, feel free to start making counter arguments; this suffices as an introduction to the angle I'm taking. Forgive the weird formatting, couple of the links weren't displaying properly and idk why.
Quick addition: anything shown from other manifestations of Battler is there to illustrate the functioning of Endless Nine or the interactions of conceptual attacks in Umi between beings of similar levels of power and the same level of existence.
