This is a Slitherlink on a hexagonal grid, with the hexagonal version of the Even Rows/Columns variant; in all three directions perpendicular to the edges (i.e. consisting of adjacent cells in the same direction), the number of cells inside the loop must be even.
This failed so much the first time I tried to make it that I almost worried the genre was literally impossible to construct, but then realized that was very unlikely, made a loop satisfying the condition, went back to the clue pattern of my first attempt, and constructed this…almost. You might be able to tell where I had to sacrifice for the sake of uniqueness.