This study examines the levels of linguistic change and Japanese contact in the stage of acquisition, maintenance, attrition, and loss of the L2 acquired in childhood through a comparison of sentence-final particles in Korean returnees’ from Japan and colonial Japanese in the incubation period. It describes the similarities and differences between frequency and function. As a result of analyzing the discourse of two Korean sisters and the translation survey, it was possible to derive the following characteristics: 1) In the overall usage of sentence-final particles, there is a significant number of casual styles. Looking at the differences according to age, KB with a low Japanese contact level is more likely to be influenced by inter-language pragmatics than KA; 2) It is confirmed that during the declining Japanese phrase much of the natural uses shown in the acquisition period were lost. However, in addition to the basic usages, additional usages were observed. They have the same operational ability as native speakers and potentially maintained in the fifth (=reconstruction) stage. Comparing to colonial Japanese or learner's Japanese, there is little misuse due to the influence of transfer; 3) In view of the appropriateness of L2 loss process in sentence-final particles, it is possible to see the stages such as ‘learners’ Japanese> returnees’ Japanese> colonial Japanese’ while the listener-aimed particles are first forgotten. Nevertheless, these are tentative. However, due to individual differences, certain particles may be used more by specific speakers.