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Tsouic is a group of three Austronesian languages spoken in south-central Taiwan: Tsou, Kanakanabu and Saaroa; plus Rukai. Within Tsouic, Kanakanabu and Saaroa form a southern branch, coordinate with Tsou.
Shared innnovations of Tsouic in sound change and morphosyntax were detailed in Sagart (2014 ) (here, sections 5.2 and 5.2, pp. 19-20).
At least 57 Tsouic-only lexical items reconstructed to Proto-Tsouic by Tsuchida (1976) are probably innovations (see the list here, section 5.3, pp. 20-21).
In addition, Proto-Tsouic *ramuCu ‘hand’, from PRT *ramuCu ‘finger’, displaced PAN *qa-lima ‘hand’. This word belongs to the most basic vocabulary: the likelihood that it was borrowed from another language, or that it is a retention from PAN is practically nonexistent.
The unusually large number of innovative Tsouic words implies a very long period of almost complete isolation in the southern part of the Formosan ridge —perhaps three thousand years—between the separation with Rukai and the breakup of proto-Tsouic.
Tsouic languages also share the metathesis of *pataS ‘tattoo, write’ to Proto-Tsouic *tapaSə (Kanakanavu tapásə, Saaroa taa-tapa-a, Tsou ta-tpos-a ‘pattern, design’).
Sagart, Laurent (2014) In Defense of the Numeral-based Model of Austronesian Phylogeny, and of Tsouic. Language and Linguistics 15(6) 859–882.
Tsuchida, S. (1976) Reconstruction of Proto-Tsouic phonology. Tokyo: Study of languages and cultures of Asia and Africa monograph series N° 5.