訓 かなら(ず) ・ 音 ヒツ
Sino-Vietnamese: tất
Looks like a heart 心 pierced by a slanting stroke: once your heart is set, it is certain, so it means invariably or certainly (Han Viet tat, as in tat yeu = inevitable).
Stroke data: KanjiVG (CC BY-SA 3.0) — kanjivg.tagaini.net
明日は必ず来てください。 (あしたはかならずきてください)
Please be sure to come tomorrow.