The story is a nice mix of Trigun and Cowboy Bebop. It starts with 10 episodes where Van, a badass with a black treanch coat in the desert with a mecha that comes from space, and Wendy are basically questing and looking for someone; Van for the man that killed his waifu and Wendy for her brother. When they reach him the plot gets serious. A lot of characters are introduced; every one of them is a very interesting one with their life goals and ambitions. But the best part about the show is the shounen parody; know those annoying speeches villains have before the fight? They are stopped sometimes even by them getting cut in half. Comrade, the main villain, is extremely charismatic and often wins people over to his side. But not Van. He refuses to lisen to them and is blinded by revenge. That is what makes this show different and fresh.
The animation was very nicely done, the character design was awesome and the mechas were very well designed. The setting is a desert planet called Endless Illusion. It is a nice mix of Wild West and sci-fi. The fanservice is here but it is not overdone and no there are no moe characters for ya fanboyz.
The sound was interesting but was nothing special. The opening looked very good and sounded nice. The ending was much better. The song is performed by an acoustic guitar and a male vocal.
Now this is the part that gives Gun x Sword its interesting flavor. We have strong contradictions in four main characters, Van and Wendy and Ray and his younger brother. Van and Ray are blinded with revenge, having lost all other meaning in life; Wendy and the kid are full of hope with aspirations for a happy, full life. There are many other characters, most interesting ones being The Claw (also known as Comrade) who wants, well to be a god and Priscilla who is a young talented pilot who falls in love with Van.
All in all this anime is one of my favorites. While taking a lot of elements from Cowboy Bebop and Trigun it gives those elements a nice twist and brings us a great story I would highly recommend checking out.