More formal variants are keredo and keredomo. The latter form is generally restricted to writing Japanese nowadays. It's also possible to use this term to refer to a spiritual violation or defilement. 43. kokoro - heart. Refers to mankind as a species, especially when contrasted with alien races, demons, elves, etc.
Men have the option of using the reduced form ossu in casual speech.
Saa - a noncommittal reply indicating that one has understood a statement and given it serious thought. Yahari, on the other hand, refers to situations proceeding as expected or dreaded. Yappari is a more casual variant of yahari. The term cuts across all classes and occupations, and must be translated according to context. The other two are suteki and subarashii.