inexpiable

Impossible to expiate or atone for.

Implacable.

Not to be expiated; admitting of no expiation or atonement: as, an inexpiable crime or offense.

Not to be satisfied or appeased by expiation; implacable.

Admitting of no expiation, atonement, or satisfaction.

Incapable of being mollified or appeased; relentless; implacable.

both unforgivable and inexplicable

incapable of being atoned for