noun which may take the genitive case particle 'no'
heart-breaking; grueling; killer
Describes a physically punishing slope, course, or exercise that feels like it will break your heart. Often used in set phrases like 心臓破りの丘 (heartbreak hill) or 心臓破りの坂 (killer slope).
A heart-breaking hill awaits at the end of the marathon course.
This training is a grueling workout.