forget, lie, cheat, deceive
諼 centers on deceptive speech: lying, cheating, or deceiving through words. The meaning 'forget' is a less common extension, possibly from the idea of words that cause one to forget the truth.
諼 combines 言 (speech) with 爰, which likely contributes the sound. The character is associated with deceptive speech, but the exact historical development of 爰 in this context is uncertain.
The left side 言 means speech, and the right side 爰 looks like a hand reaching out. Imagine someone using smooth words to reach into your mind and deceive you, making you forget the truth.
For ケン, imagine a con artist named Ken who uses deceptive words to cheat people: Ken -> ケン, and his lies are the speech 言 on the left.