James Brennan

James is Bobby's uncle, and part of the side story, Louder than Love. He is on Bobby's dad's side, and was originally a Sullivan as well, but he thought it was best if he changed his surname to avoid getting his brother involved with what he was doing.

Titan
James was the previous wielder of the Attack Titan, which means he could turn into a 15m, stronger version of himself which also granted him new abilities. He could see all the previous Attack Titan Shifter's memories, and could also harden himself with a crystal like substance. As well as this, he had advanced healing from any and all wounds as long as he wishes to do so and immense strength. Some of these, like the healing and memories can be used while he was human, and could even learn how to harden as well, but will take a lot of training to do.

Backstory
James was born in Southend, England and was one of three brothers, being the middle one. Their parents largely neglected them, and as such the brothers grew very close to each other. However what they didn't know, was that their parents were focussing on staying hidden from groups of people that wanted them dead. This was because James' dad was a part of a secret organisation called the brotherhood, which were mainly vigilantes. They wouldn't go out of their way to stop crime, but they would go after large drug empires, and either take them out secretly, or dig up dirt on them to get the police after them.

This got their organisation hated, and so the mafias managed to corrupt the government, so that they were now after them as well. Despite his dad's best efforts, James managed to find out about this, and tried to convince his dad to let him join. To which the answer was always no. This was because the dad was more interested in letting Robert (The oldest brother, and Bobby's dad) join instead due to him being much more mature. However Rob was never interested. Rob personally hated the organisation, since he had known about it since birth. This was because his dad had tried indoctrinating him, trying to not only get him into the brotherhood but to become a candidate for the Attack Titan. However James never found out about this till much later when he was finally let in, though not to inherit the titan since the current holder was only interested in making Rob the holder.

Years past, and James was finally let in at the age of 16 and was even out through the trial to inherit the titan shifter as the current one was on the verge of getting found out. However their youngest brother, Michael, was found dead underneath the brotherhood. This really pissed off Rob since not only did his brother get murdered by the people the brotherhood were fighting, but his parents had endangered him in the first place for even being involved. The final straw was when his dad refused to even hold a funeral over fears of "drawing suspicions". Rob went to the enemy and told them everything, about their location, their members and even about the attack titan. Though by this time the titan had been passed down to James who had escaped to Seattle where he lived in peace until around his early twenties where the cast was clear for him to start rebuilding the brotherhood and keeping an eye on Bobby.