WARNING: The following contains spoilers for Mass Effect 3.
In the Mass Effect games, Commander Shepard recruits a variety of skilled aliens to his team, including the Drell assassin Thane Krios. And Thane has some family drama to settle.
Despite being a lone, wandering assassin, Thane was once a family man, and he hasn't entirely lost those familial ties. He has a son, Kolyat, who feels lost in the world, and weighs heavily on Thane's mind. It's up to Commander Shepard to help father and son reconcile and find happiness and peace at last.
A Fleeting Household
Thane grew up on Kahje, training from the age of six to become a ruthless assassin, a living tool for his employers and clients to use. As a man, he performed this job well, but one mission changed everything. Another Drell, a woman named Irikah, spotted Thane's target and shielded him, defying Thane's sniper rifle with determined eyes. Intrigued, Thane awoke from his "battle sleep" and sought out Irikah. What he found was something wonderful. She forgave him, then came to love him, and he loved her equally. They were soon married and had a son, Kolyat.
However, Thane wasn't prepared for fatherhood, and he served as a freelance assassin on long missions, meaning Irikah largely raised Kolyat herself. One day, while Thane was away, Batarian thugs and a human assassin named Stiv Kay retaliated against Thane by cornering his family. Kolyat took shelter, but Irikah was killed. When Thane found out, he tracked down those responsible and tortured them, something he'd ordinarily never do. For once, Thane acted in anger and self-interest, and he left all the assassins dead. He resumed his work in a battle sleep and lost contact with Kolyat. Later, in 2185, Thane was carrying out what he thought would be his last mission: assassinating Nassana Dantius on Ilium. Then he crossed paths with Commander Shepard.
The Reconciliation
One day, Thane is passed a message about his grown son, Kolyat, who is desperate to reconnect with his father. Kolyat is on the Citadel and has taken a job from the human mobster Elias Kelham to assassinate a Turian political candidate named Joram Talid. But Kolyat's mission is more about getting Thane's attention than actually serving Elias Kelham's interests. It works: with Shepard backing him up, Thane visits the Citadel, tracks down Joram and confronts a gun-wielding Kolyat in Joram's apartment. C-Sec arrives, and Kolyat is taken into the custody of C-Sec officer Bailey.
Thane and Kolyat are slowly but surely mending ties when Thane explains his side of the story of Irikah's death. Kolyat now has a complete picture, and no longer blames his father for being absent and leaving the family vulnerable. Over time, their bond strengthens, and by the events of Mass Effect 3 in 2186, they are on good terms. Kolyat often visits his father in the Huerta Memorial Hospital, and Thane is grateful for the company. Then, Councilor Udina launches his Cerberus-backed coup.
Thane gives his life to help Shepard foil Udina's plans, fighting Kai Leng hand-to-hand despite his failing health. While Thane is near-death in the hospital following the fight, Kolyat is there keeping his father company. The younger Krios invites Shepard to help with traditional Drell funeral rites, and Thane is honored as he passes away in peace. Kolyat grieves for his father, but otherwise, he takes it well. He is strong of spirit and on good terms with Shepard. Kolyat will remember his father fondly, and he will assist Shepard however he can.
Thane thought that he only had the life of a lonely assassin ahead of him until he met the love of his life and found happiness. Then, it was all taken away, and he was ready to give anything to have that happiness back. Kolyat's position is rather similar: he grieved for his slain mother and raged against his seemingly neglectful father. Through rash means, he tried to get that happy family back together. Both Krioses were rather unprepared for the hardship inflicted upon them, but through their renewed faith in others, they mended ties and learned that the future always outweighs the past. Thane moved on from his rage-fueled retaliation against Irikah's killers, and Kolyat freed himself of his rage toward his father. In short, Thane and Kolyat both proved that it is never too late to have hope, and that past wrongs don't have to poison the future.