Disclaimer: I do not own Shakugan No Shana.
The following story takes place after the final conflict in episode 24 when Shana and Sakai go to school. My take on what should have happen.
Revised: August 25th, 2009
It amazed Yuuji that the city could look so beautiful and untouched after it faced destruction just a few short hours ago. He had never realized that despite the buildings sturdy frames, unique culture and wonderful people this city had to offer, they could be wiped out and forgotten in an instance. Humans were fragile things and they only had a short amount of time to leave their mark on this Earth. Had it not been for Shana, many of this city's inhabitants would have been robbed of the opportunity to truly live their lives. Looking at the girl walking beside him, he wondered truly if she had summoned Alastor as her duty as a flame haze or did she really love this city as much as he did?
"Misaki City has always been my home… I love this city to the point where I would give my life just so it could continue," Yuuji said.
Shana looked at him strangely, before saying "I thought you were willing to leave it."
"I was and still am, willing to." Yuuji said. "But I was thinking… About what you said to me, when you told me that you loved me… And I think… That I love you too."
"W-what?" Shana said blushing.
"I know I love you Shana," Yuuji said with more confidence. "Because I was willing to give up this whole city, not only so it could continue… But so I could still be… with you…"
"Yuuji…" Shana started, realizing that this was not an opportunity to miss, "This is something I should have done as soon as I realized it…"
"Huh?" Yuuji asked confused.
It was at that very moment, for the first time in history, that a flame haze ever kissed a mistes. It was brief and amateur, but by the time the two actually reached the school they had become something of kissing experts with all of their brief stops.
It would also be in years to come where Shana would officially change her name to Sakai Shana and the two would be known as the best Tomogara and Rinne fighting duo.
But until then, a short while after the kiss, the two headed to school, with Shana confidently thinking 'I always win'.
And let it be said that Shana and Yuuji, despite leaving earlier than normal for school, came in rather late.
And that is the tale of Shana's first kiss.
Revision: I revised this story significantly on August 25th, 2009. I changed sentences and fixed grammar mistakes. The story line has been left the same. I'm aware that depending on the translation Sakai's name is either spelt "Yuuji" or "Yuji". I've left it the same because the translation I got spelt his name "Yuuji".