Masane's sealing technique would delay the curse technique's usefulness for several reasons. The first, by absorbing the chakra from the technique itself, and secondly by preventing Eric from actually surging chakra into the portions of her shadow where the fuinjutsu affected. Outside of the radius of her seal, however, Eric's shadow curse would still be in effect, and considering the conjoined nature of the shadows of the plains, it would only be a matter of time before Masane would have to once again be concerned with Eric using his shadow directly against her. But time was always something well bought; it would be remained to be seen if it would be well spent.
Nonetheless, without being able to directly restrain her with his shadow, and beginning to notice a pattern with her fighting style, it was evident that he needed to prevent her from being able to look at him directly before he could consider a plan for going on the offensive. Which was easier said than done.
Before Eric could put his mind to that, once again, the barrier for Kamui reached his space, except this time, it was going directly for his chakra cloak and body. Swiftly, two of Eric's tails flew directly between himself and Masane, blocking her eye contact with him and sparing him death by space-time beheading. Sure, the Kamui, if she proceeded to focus her eyesight, might would take his two thick tails, but that would allow Eric to perform a set of handsigns without losing his head.
Not to mention the tails would subsequently grow back, since it was only the V2 tails. His handsigns complete, Eric's chakra would once again be at work through the air, shrouding the majority of his immediate area (about a 40m diameter in a spherical shape with himself as the moving epicenter. Thus, it extends 20m upwards at its highest) in darkness. Using his chakra to absorb rather than refract light, he would shroud the aforementioned area in darkness.
Yamigakure no jutsu; Hiding in Darkness Technique
He wouldn't need to have his chakra in every inch of the area afflicted by a decrease in visible light, however, since if he absorbed the incoming light from above, that darkness would extend downward like a tree branch shading the forest floor. The only place he needed to constantly have chakra would be areas between him and Masane similar to the Hidden Mist Technique, in order to further hinder her ability to use Kamui against him. This artificial shadow, naturally, would have been more useful if he could use his Nara techniques directly on Masane this time, but using his chakra (and the darkness) to prevent Masane from even seeing him was the crucial point of this technique. Additionally, thanks to the broad daylight, once a sufficient amount of heat had accumulated, the technique would require less chakra for Eric to maintain the technique. Since he was in his tailed beast v2 cloak form, the switch from daylight to practical nighttime would be like a flip of the switch, the afflicted areas resembling a starless, moonless night.
Since the affected area was, for all intensive purposes, a giant shadow, almost anywhere within it Eric would be able to detect movement and general disturbances, thus making up for the worsened conditions for eyesight. Were his quarry to remove herself from the affected area, she would only be able to see a shroud of chakra when looking in towards her perceived target (and of course a dome of darkness/shade). Eric would still be able to track her thanks to him cursing the fields from earlier, but at least she would not be nigh blind any longer and within his playing field.
Upon landing on his feet, the man would proceed to attempted to shadow migrate 20 feet behind himself, in an attempt to further disorient his opponent. However, the man did not shadow migrate, but instead, got a DoS sort of response from his gate. Realizing that he was unable to use shadow migration for some reason or another, the man had to conclude that it had to have been something that his opponent had done.
That first non-Kamui scroll did not seem to have any pertinent effects on the surroundings, unless it was the culprit. Recalling this and piecing it together, Eric would assume that the first unsealed scroll had likely been the culprit. He would make a note that at some point he needed to either neutralize that scroll or end the fight.