Irarutu, Irahutu, or Kasira is an Austronesian language of most of the interior of the Bomberai Peninsula of north-western New Guinea in Teluk Bintuni Regency.

[2] The name Irarutu comes from the language itself, where ira conjoins with ru to create 'their voice'.

[4] There are seven variations found within the language: Nabi, Babo, Kasuri, Fruata, South-Arguni, East-Arguni, North-Arguni.

Voiced stops /b, d, ɟ, g/ are mainly heard as prenasalized [ᵐb, ⁿd, ᶮɟ, ᵑɡ] in the Fruata dialect.

/f/ is found in all three positions and is sometimes pronounced as a voiced [v] by Native Irarutu speakers, and is mainly heard as a bilabial fricative [ɸ] in the East Arguni dialect.

Adjectives such as big or a numbered value come after the noun, but for lineage-related matters the initial ancestor comes before the descendant.

[2][3] Nouns are words that can be placed in the subject or object portions of a sentence and can be modified for possessive relations.

In Irarutu, the grammatical function for nouns and pronouns do not differ for unique situations.

The only cases where changes to the word are made are for body parts, names, and one's child.