I am finishing an arc of my novel, and right at the end some sudden development happens with MC, that is partially obscured from the reader. They can guess at what it is, but it is a sudden change to MC outlook and demeanor.
I'd like to move the story forward and start the next arc some time later with the support cast, showing some changes to the world and then later return to MC and reveal his change, to cause a huge impact (tentatively).
This development will cause surprise to the support cast because they are ignorant of that sudden MC development. My intention is to get the reader to share that surprise along the support cast during the big reveal.
But to do so, MC has to go a few chapters without showing up. Readers might complain about his whereabouts.
If I don't do the short timeskip and skip to the support cast and let the narrative follow the MC, the reader will already know when the reveal is done.
How should I structure my narrative so (assuming they won't guess - they probably will) the reader can be surprised together with the support cast during "the reveal".
I'll make one example using a wuxia story (mine is not wuxia):
Shen Ling is wounded and tired. He was separated from his companions, and ended up seeking shelter in this tomb he fled to alone during the evacuation of the kingdom due to demon attacks. Then he finds an ancient scroll in the tomb depths. Chapter ends.
Fast forward a few months, the gang is settled in another kingdom that is going to host a martial arts tournament soon. Warriors from all around will gather to fight, including some from the demon kingdom that made the gang refugees. We follow their antics, how they settled in this new home and how they miss MC. But for dozens of pages, MC is nowhere to be seen.
The demons want to get the princess because it is demons and princess and plot they harass the gang and set up a trap. A mysterious contender that is in town for the MA tournament rescues then and vanishes before they can give their thanks (or ask who he is >.> ).
The mysterious contender and the gang+princess meet several times. The stranger seems interested in the princess, but her irritation gets her to the point of almost breaking into a fight. But the demons' plans are repeatedly thwarted because of the contender's intervention, even though it is not clear for the gang at the time.
MA tournament comes, and both princess and contender move forward as they win their fights. Contender defeats demon representative, and faces the princess in the final round.
During the fight it is revealed that contender is actually MC, that he spent months trapped in the tomb studying the awesome MA techs in the scroll, and he learned of the demons plans. But he had to achieve goal X without anyone suspecting his identity (he is rather infamous, if people knew who he was from the beginning, goal X would be unattainable). Since the gang was closely monitored at all times, he couldn't reveal himself to them either.
I think the princess still beats him out of sheer anger (angry heroines add her girl power to damage), but our example ends here.
The reveal is both that contender is MC in disguise (this is rather obvious and cliche, but its fine) and the other hidden reveal is goal X. I think it would be impossible for the narrative to follow MC without giving out goal X.
What writing techniques can I use to make this kind effect? how can I keep the reader interested when MC is MIA for a long time (both in universe and in # of pages).