It starts as most things do, unexpectedly.
Well, as it happens, it mostly starts because Shepard, Hela, is too stubborn to ask for help.
Garrus knew, the second he saw her, he knew that she was Shepard. His Shepard, their Shepard - not some Cerberus clone or rebuilt machine. Just living, breathing Shepard.
Kaiden broke a bit of that Shepard.
She throws herself into work, partially fighting the Collectors, partially fighting Cerberus in her own passive aggressive way - amusing and awe-inspiring in many ways. Garrus know's how ruthlessly charming and fantastic she can be, he just never thought he'd not want to see it.
So, at the end of the day, it starts with her being stubborn.
She forgets to eat, sleeps only a few hours a night and soon that takes a toll. They're all worried, but they don't know her. Not how she was, how she could be if she allowed it.
She's scared, and Garrus doesn't like a scared Hela.
He begins slowly, not wanting to scare her more. She thinks she's an imposter. She doesn't think she's really Shepard, but she's just a little slow on the uptake and that's ok. They've got a little time.
So he begins slowly, leaving little bites of food on his plate, 'I can't finish it all, Shepard?' and watches with hidden glee as she takes bites without thought.
Soon, it's 'Here Shepard...' and a plate of whole, hot, freshly made food taken with a weary smile.
Soon, it's 'Shepard, come look at this...' and 'Shepard, come watch this...' just for him to watch as her eyes grow tired and her posture slumps, breaths deepening to sleep as she leans against the wall or his shoulder.
Soon, she smiles brighter, laughs a bit and bonds with the rest of the crew. Introducing him to Grunt with a fond smile, a 'my crew, my people' kind of smile.
Eventually, it's his name she calls first, his brain she racks for plans and his presence she wants by her side.
Eventually, it's their picture on her bedside table, and him in her bed.
Now, it's just them.