This is the 7897th most frequent Japanese word.
在りし
"在りし" means "former" or "past," often referring to a time in the past or something that once existed.
In this sentence, '在りし' is an archaic word meaning 'the past' or 'former times,' used to talk about past days or times nostalgically.
在りし日の思い出が蘇る。
Memories of days gone by come back.
Here, '在りし' is used to describe something that existed in the past, in this case, referring to his former family, implying they are no longer together.
彼は在りし家族の話をするのが好きだ。
He enjoys talking about his former family.
In this context, '在りし' reflects on the state of the world as it used to be, emphasizing the contrast with the current state.