This study, as one of the first in its kind, focuses on code-switching in computer-mediated communication (CMC) among Gen Z Japanese Americans who have been simultaneous bilinguals since childhood. We collected a dataset of 1,561 online text messages that were exchanged between these bilinguals and found intriguing code-switching patterns not typically observed in spontaneous speech nor reported in the literature. First, we find a surprisingly high portion of Japanese usage in the dataset and noticed high occurrences of Japanese auxiliary verbs and low occurrences of Japanese pronouns compared to the English counterparts. The data suggests these bilinguals have a strong grasp of both languages and are actively code-switching to construct their bilingual and bicultural identity over text. Second, our data shows that preferences for a type of code-switching (intra-sentential or inter-sentential) when texting friends are not a reflection of language proficiency or constraints of the CMC medium, but rather reflect the frequency with which the speakers orally code-switch and speak the embedded language at home. Moreover, we observe the speakers’ development of a CMC style of Japanese-English code-switching through using romanized Japanese words, elongating Japanese words using romanization, mixing writing scripts, and writing English words in Japanese characters.