An innie and an outie whose difference is fixed by the 45-rule. hard killer only
By the 45-rule over the tinted rows/columns, the innies minus the outies of the cages must balance to a fixed total; values that break the balance, 1 and 6 in R2C8, R3C4, are struck.
Comparing a unit's 45-total against its cages sometimes leaves one cell poking in and another poking out. Their difference is fixed by the sums, tying the two cells together and erasing every pencil mark the relationship cannot reach.