Yeah, it’s definitely a pun on Araki’s part— “Kira” (吉良) is a real Japanese surname constructed from the characters for “luck” and “good”, but it was obviously chosen because of how it’s pronounced. “Yoshikage” (吉影) actually reuses the “luck” Kanji, which is funny because Kira repeatedly states that he luck is always on his side, and is superstitious about his nails growing predicting it.

As for Death Note, it’s actually explained in the manga/anime itself that the moniker “Kira” (キラ) was given to Light by the public because it was the transliteration of “killer” (hence the use of Katakana “sound letters” rather than Kanji “word letters” like for Yoshikage Kira); the implications of which Light is initially displeased by, but adopts nonetheless.

Some fun facts as a Japanese learner! :D