Who pulled out the Z Sword?
During the game's Majin Buu Saga, Gohan is brought to the Sacred World of the Kai to remove the Z Sword.
While it turns out the extremely heavy blade is useful for little more than training as it is incredibly brittle, there is a surprise waiting inside once Gohan accidentally breaks it. From there, it's revealed that Old Kai was sealed inside the sword many years ago.
In the Dragon Ball Super manga, Future Trunks obtains the Z-Sword and masters it while training with Future Shin and Future Kibito. However, the Z-Sword is later broken after it is turned to stone by Future Dabura's Stone Spit (which leads to Future Old Kai's death).
During this meeting, Old Kai and Beerus fell into an argument. Though the verbal spat enraged Beerus, it would have been inappropriate to eliminate the Sacred World of the Kais. Thus, the God of Destruction sealed the Old Kai in the Z Sword, embedding him in what would become the Z Sword Plateau.
Gohan and the Z Sword
However, the reverence of the Z Sword is quickly traded in for some father and son shenanigans once Goku arrives. The Kai are left speechless when Goku can also lift the sword, giving the impression the mystical weapon might not be that special, but rather the Kai are just weak.
Gohan then tries to pull out the sword and falls back on his head with his hands pounding red. After the failed attempt in his normal form, Gohan gives it a go again and turns into a Super Saiyan 2. With his strength, he pulls it out, also managing to ruin a bit of ground around it.
The life link also serves to keep the Gods of Destruction from killing their weaker counterparts, as Beerus chose to seal Elder Kai (an active Supreme Kai at the time) in the Z Sword as killing him or destroying the Sacred World of the Kais would have been improper and dangerous.
The Z Sword was stated to have the ability to grant whoever pulled the blade from its resting place an incredible power, believed to make them strong enough to defeat Majin Boo by Kibito. It was reputed to be the "strongest of swords".
When Goku was trying out the Z sword he commented that it was heavy but he was able to swing it around and even pass it back to Gohan with one outstretched arm. So the sword must have weighed less 10 tons, it couldn't be considerably more than that.
Why is Future Trunks hair blue?
For the anime adaptation, Bulma's hair was made blue while Trunks' was kept purple. By the time of Battle of Gods, Akira Toriyama had begun coloring both Trunks & Bulma with blue hair– not purple. While Toei kept kid Trunks' hair purple, Future Trunks' hair was made blue to match his modern character design.
Gohan loses the use of his arm in his final battle with Cell when he tried to save Vegeta from a blast intended to kill him and Future Gohan loses his arm completely after protecting Trunks from the androids.