Butsu in Chinese / Japanese...

This is the modern Japanese version of "Namu Amida Butsu" or "The Compassionate Amitabha Buddha".

Some will translate this as, "I sincerely believe in Amitabha; Lord have mercy on me".

This phrase especially applies to Japanese Pure Land Buddhists.

There is a more universal version using ancient characters (with more strokes) for the 4th and last characters. That version is also used in Chinese, Korean, and occasionally Vietnamese. This is used to pay homage to Amitabha Buddha.

See Also:  Bodhisattva | Buddhism | Nirvana

This is how to express "The Compassionate Amitabha Buddha" (especially for the Pure Land Buddhist Sect).

Some will translate as, "Homage to Amitâbha Buddha" or "I seek refuge in the Amitâbha Buddha".

This is valid in Chinese characters Japanese Kanji, and old Korean Hanja.

Sometimes modern Japanese use a different version of the 4th and last Kanji but the version shown here is the most universal.

This is used to pay homage to Amitabha Buddha.

See Also:  Bodhisattva | Buddhism | Nirvana

仏 is the single Japanese Kanji can mean Buddha or Buddhism.

This Kanji was actually a shorthand way to write 佛 (Buddha) in Chinese (popular around the 13th century). Somehow, this became the version of this Chinese character that was absorbed into Japanese, and thus became part of standard Kanji. Centuries later, this character is not recognized in Chinese at all (except by those from China with a background in Chinese literature or language).

仏 is also a rare or derivative Korean Hanja form - but I doubt you will find any Korean that knows that.