既 means already and is a JLPT N1 kanji. It has 10 strokes and uses the choking on breath radical (旡).
Stroke order · 10 strokes
On'yomi (音読み)
キ
Kun'yomi (訓読み)
すで(に)
Radical
旡 · choking on breath
Strokes
10
How to remember 既
Having finished eating and turning the face away — it's already done. 既に (already); 既読 — the 'seen' mark on LINE; 既読スルー means seeing a message and not replying!