Circumcision, Water Immersion and Purim

For the Jews it [the fourteenth day of Adar] was a time of happiness and joy, gladness and honor. In every province and in every city, wherever the edict of the king went, there was joy and gladness among the Jews, with feasting and celebrating. And many people of other nationalities became Jews because fear of the Jews had seized them. [Esther 8:16,17]

And the Jews had light and gladness in every city and province where the decree was published; wherever the proclamation was made, the Jews had joy and gladness, a banquet and a holiday. And many of the Gentiles were circumcised and became Jews out of fear of the Jews [Esther 8:16, 17 LXX]

And then from Donaldson's Book:

The world reflected in LXX Esther, then, is one in which the possibility of proselytism can be taken for granted, even if the role of the proselytes in the story is just to underline the reversal of fortune that the Jews experienced. But is this the extent of their role in the story? There is additional evidence a little further on that suggests a more positive attitude towards proselytes and their significance for Israel. The outcome of the story, of course, is the establishment of the feast of Purim. When the vindication of the Jews has taken place, Morecai and Esther decree that "these days of Purim should be a memorial and kept from generation to generation, in every city, family and country." (9.27) The result is that "the Jews took upon themselves, upon their descendants and all those who would join them to observe it without fail. Clearly, "those who have joined them" are proselytes. The connection with 8:17 is equally clear; just as many Gentiles joined the Jewish community during the climactic events themselves, so it is expected that "those who have joined" the community will take a regular part in the commemoration of those events. While fear may have been the motivation for their conversion, fear is not a negative thing in LXX Esther (1:22, 2:20, 15:13). The Judaizers of 8:17 are to be seen as full converts, those "who have joined" the community of Israel.

The LXX is positive in its attitude towards proselytes, taking it as a matter of course that the Gentiles will be drawn by Israel's success and seek to convert.