And he's a ninja! In Naruto, they do 15 impossible things before breakfast! This sort of line would make sense if Shikamaru didn't personally have the ability to move and kill with his own shadow.
Oh yes, and this.
Shikamaru's initial reaction should probably be something along these lines:
Obviously a jutsu. There were three basic types: taijutsu, genjutsu, and ninjutsu. Taijutsu was obviously out for the same reason it had to be jutsu in the first place. That left genjutsu or ninjutsu.
Consider genjutsu: illusion. Hidan might really be dead, but then he couldn't maintain the illusion; perhaps the illusion was Kakuzu's. Alternatively, the wound could be illusory, or the body itself. Hidan might be uninjured, or somewhere else.
If it was ninjutsu... they were basically screwed. Any technique that could actually prevent death would have to be kinjutsu, a forbidden technique. He'd have to run. Actually, he should probably kill Asuma himself, just in case the kinjutsu prevented his soul from reaching the pure world...
Shikamaru could feel himself flinching away from the thought. No, he told himself. If that was really what was at stake, he had to know. He would not sacrifice Asuma's soul because he was too cowardly to admit that he could lose.
Kinjutsu or genjutsu. Everything depended on this. How could he find out?
Yes, that's definitely a fragment from a better Shikamaru vs...; on the other hand, I don't remember that battle too well, wasn't the immortality thing an actual immortality? So by your reasoning above Shikamaru couldn't've won (since it was a ninjutsu/kinjutsu).
Presenting: Shikamaru vs. the Logical Fallacies, a rationalist fanfic set in the Naruto universe and starring a realistically rational Shikamaru. The writer is a friend of mine going under the alias FanFicBias, and I am an editor along with the author.
We welcome reviews on FanFiction.Net and both reviews and discussion (naturally) are welcome here. We are looking to improve our work, so please be as honest and as harsh in constructive criticism as you like. Praise, however, is also always welcome!
This story does contain SPOILERS for the Naruto series. Readers who are unfamiliar with Naruto may have a hard time understanding what's going on, but it would still be interesting to hear from non-Naruto fans, since perhaps we can ameliorate this issue with the aid of constructive criticism.
We do strive to follow the First Law of Fanfiction and the Rule of Rationalist Fanfiction, so please call us on it if we fail to do so.
http://www.fanfiction.net/s/6781426/1/Shikamaru_versus_the_Rational_Fallacies
Note: Thanks to all reviewers and participants in this discussion! We're trying hard to make Part 2 even better.