The characters /ya/ and /wa/ occur frequently in Batak manuscripts from all regions.
This is in spite of the fact that in Toba Batak the semivowels [w] and [j] only occur in a limited number of mainly Malay-Indonesian loanwords such as mawas (orangutang), bawang (onion), or layar (sail).
In all Batak manuscripts, regardless of their regional provenance, the semivowels /ya/ and /wa/ are frequently used as a glide to link the vowel combinations ea or ia (written eya and iya) and ua, ue, or ui (written uwa, uwe, and uwi), but other combinations are also possible: the word naek ‘ascend’ is spelled alternatively nayik and nayek in the same text (Voorhoeve 1975:135). The common words dua ‘two’ and ia ‘if’ are almost universally written /duwa/ (ᯑᯮᯋ) and /iya/ (ᯤᯜ), and only occasionally ᯑᯮᯀ and ᯤᯀ.[w] and [j] are common phonemes in modern Indonesian: Saya wanita [saja wanita] means “I am female” in Indonesian. Toba and Simalungun Batak did not use to have these two semivowels, but all Batak languages nowadays have many Indonesian loan words.
The semivowels [w] and [j] are hence a rather recent development in the Toba and Simalungun Batak sound-structure. Lopez (1939 : 17) does not include them in his list of Toba-Batak sounds. The semivowels came into Toba and Simalungun Batak through mainly Indonesian-Malay loanwords and through the contact of its speakers with other languages.
The letter /ya/ is a regular feature in the Mandailing Batak dialect, and in both Karo and Pakpak the semivowels [w] and [j] do regularly occur.
The shape of /ya/ is in all Batak languages the same: ᯛ. In Simalungun the. two elements are not connected: ᯜ.
The words pea (swamp) and rea (great) are common words in Simalungun and Toba. They can be written ᯇᯩᯀ and ᯒᯩᯀ (the horizontal dash on the top left of the letters /pa/ and /ra/ is the diacritic for [e]).
Even though the /ya/ is not really needed in Simalungun and Toba because they lack the phoneme [j], the character /ya/ is frequently used as a glide vowel. The above words pea and rea can also be written ᯇᯩᯛ /peya/ and ᯒᯩᯛ /reya/ even though the pronunciation is [pea] and [rea].
In Karo, the word for ‘swamp’ is paya which is of course written ᯇᯛ.
The shape of the letter /wa/ is the same in all Batak languages ᯋ. In Simalungun the lines typically do not connect and hence we have the shape ᯌ. In writing the letter /wa/ is indeed written using three strokes. First the long and curved upper line before the two short horizontal strokes are added.
In all Batak languages the letter /wa/ is commonly used to connect [u] with [a] and [e] with [a].
In some manuscripts originating from Pakpak and Toba the shape ᯍ is used instead of ᯋ.