Sebastain plz XD I think Sherlock relates to that "how do I pretend not to be me?" part on a smaller, human level.
-- With Sherlock's ability to read others, it's always good for me to read the stats and backgrounds of different characters, especially those I'm canonblind to. Because Sherlock may be able to pick on these details naturally, but I have to actively work to make a believable observation and to be able to connect the dots on things.
I research. A LOT. Not even just characters, but the worlds they come from, what their time periods were like, etc. I try to be as informed as possible so that Sherlock, who still may surprise people with his statements, is usually on point. It also helps when other players leave hints in the brackets for Sherlock to pick at. But that's basically the gist of how I handle this aspect of him.
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Having been in Kiseki a while, are there things Elsa misses from home besides her sister?