• 必かならず — surely / without fail
• 必要ひつよう — necessary
• 必死ひっし — desperate / frantic
• 必然ひつぜん — inevitable
• 必見ひっけん — must-see
• 必勝ひっしょう — certain victory

必 originally depicts clenching something tightly, symbolizing inevitability or certainty. It appears in words that express necessity, absolute conditions, or things bound to occur.