Throughout his time behind bars, Sonia has faithfully visited him whenever she can. Often, she came with their father and her daughter, who is close to Kalwant.
In order to get to Changi prison, her father would drive his taxi from their home in Cameron Highlands, Pahang, all the way to Singapore.
Together, the small family would spend the night in the taxi after reaching Changi Village before heading to the prison the following day to visit Kalwant.
He also fought hard to ensure that his son received the best legal aid possible.
He died of cancer last year, but not before clocking in 820,000km on his taxi metre.
"That was his sacrifice – he drove all that distance for Kalwant," Sonia said in a recent interview with MalaysiaNow.
Sonia said Kalwant never liked it if the visits were filled with tears.
"He hates it," she said. "So we would go and see him with all the latest news and gossip and funny stories.
"The time we spent together was always filled with laughter and happy memories."
Adding that Kalwant was more of a child to her than a brother, she said he was a loving person who was always ready to help anyone in need.
"We have been close since we were both small, always getting into trouble together," she said.
"But he is really special because he will do anything he can to help. That was what he always did for us as a family."
As for her daughter, Kellvina, she said the girl loved her uncle as he had always taken care of her.
Kellvina was only 11 when Kalwant was arrested. Even then, Sonia said, the girl seemed to understand what had happened to her uncle.
"She saw that I was always sad," she said, adding that she had been going through depression at the time.
"But she helped me so much to be at peace and to be patient. And she has never once forgotten to write to Kalwant in prison."
Now, at 21, Kellvina still faithfully visits her uncle in prison whenever she can.
She is also a happy sight for the other prisoners on death row, who have watched her come and go since she was a child.
Although they are separated by many miles, Sonia said, her daughter and Kalwant had become closer than ever since his arrest in 2013.
"From day one, I knew Kalwant loved his niece."
Never give up
Kalwant's date with the gallows comes less than three months after the execution of Nagaenthran K Dharmalingam, which took place despite an international outcry and amid increasing scrutiny of the republic’s use of the death penalty.
He had an IQ of 69, a level recognised as a disability, and was reportedly coerced into committing the crime of drug trafficking.
Kalwant himself has filed a notice of motion to the Singapore Court of Appeal for a stay of his execution as well as a review of his conviction and sentence.
His stay application will be heard by a three-man bench at 3pm today.
Sonia said she and several other family members had been in Singapore since late last week.
They came early in order to spend time with Kalwant, and to consult with their lawyer.
But despite his looming execution, Sonia said Kalwant was still positive and in good spirits.
"He won't give up," she added. "He will keep fighting his death sentence because he believes that this is not the end for him."
For herself, Sonia only hopes that her brother is truly as upbeat as he seems.
"I hope he is not pretending for our sakes, to protect our feelings."