This is the 65th most frequent Japanese word.
入っ
The Japanese word "入っ" (haitsu) translates to "entered."
Here '入っ' appears in '入ってきた', conveying the idea of 'entering' in a spatial context, specifically something moving into an enclosed space.
雨が屋根の隙間から入ってきた。
Rain came in through a gap in the roof.
The word '入っ' is used in the verb '入って', which is the te-form of '入る' (to enter). It indicates entering a location.
店に入って新しい商品を探しました。
I entered the store and looked for new products.
In this example, '入っ' is part of '入っている', illustrating a metaphorical sense of 'being included' within something.