"Unbreakable bond" refers to a very strong connection or tie between people that cannot be broken or easily severed. It indicates a deep level of trust, loyalty, and support that lasts even through difficult times. Full definition
(WBNG)-- It's a now unbreakable bond between two Southern Tier women who were once strangers to each other. (wbng.com)
Armed with knowledge and a clearer sense of the world through our children's eyes, this period of uncertainty can afford a myriad of opportunities to forge unbreakable bonds of trust and respect. (amazon.com)
As a heroic Rider, you'll form unbreakable bonds with tamed beasts known as Monsties. (nintendo.co.uk)