Chapter 1 - Backstory

He's kind of just an alien with horns

After joining the time patrol he makes a team with the mentor Hera, who teaches him about the job. Since after a timeline is "fixed" it is reset, Hera taught Jack that killing is okay since they'll just come back after the reset. Because of this he has less value for life in general and has become complacent in his power, being one of the weaker overall time Patroller's until later on in the series. Eventually Artemisia joins their team and the two quickly become friends. With no real ambition himself, Jack promises Artemisia to help her become stronger and more fluent in controlling her body. Eventually Hera dies in a mission and the two are left looking for either a replacement or a third member to qualify for the Tournament of Time.

Chapter 2 - Powers

Through chronos, Jack is able to create axes.

That's it

He can throw them

He can dual weild them

He has an attack called red x where he slashes two axes

But that's it

Side ahh character

Chapter 3 - main story

After being able to qualify, because of spoilers during the Gabi arc, Jack and Artemisia enter the Tournament with a placeholder 3rd member. They make it to the semi finals, mainly because of Artemisia and Jack has to go against Saber. Because of the wide gap in power he is unable to deal damage and has every axe he creates broken by Saber. Before he loses Saber tells him how taking the easy way out will only take you so far, killing people. After this embarrising desplay Jack trains vigorusly with Artemisia becoming a little stronger.

During one of the Athena Arcs him and Artemisia gain chronos forms, shooting them up on the leaderboards as the gap between those with chronos forms and those without are extremely high.

During the finale, ignoring some spoiler stuff for out of time, he joins Artemisia and (spoiler) against the main villian Absolom. He is able to put pressure on him but that's about it, eventually when left alone he sacrifices himself so the others can regroup.

"I wish i new about this whole world of chronos. Maybe with that kind of strength I could've made up for everything."