Sincere True Sincerity in Chinese / Japanese...

真誠 is the true essence of sincerity.

It takes strength of personality to be truly sincere without overdoing it. Speaking of strength, this is probably the strongest way to convey the idea of sincerity in the Chinese language.

The first character literally means true, real, and genuine. While the second character means sincere and honest.

See Also:  Love | Honor

至誠 is the idea that you enter into something with the utmost sincerity and fidelity. Ideas such as devotion, honesty, and “one's true heart” are also contained in this word.

至誠 is a universal word as the Chinese, Japanese Kanji, and Korean Hanja are all identical.

While 真心 literally reads as “true heart” or “genuine heart,” the understood meaning is sincerity, devotion, sincere, or heartfelt. Some will extend the meaning to be like “true love.” It's the idea of doing something or treating someone with genuine feelings.

真心 is valid and has the same meaning in both Chinese characters and Japanese Kanji.

Note: While not too common, this can be the female given name “Mami” in Japanese.

虚実 is a Japanese word that means “falsehood [and] truth” or “fiction [and] fact.”

This concept is used in warfare, gameplay, and martial arts strategies. 虚実 can be a strategy of real and/or deceptive moves. This gets to some Sun Tzu Art of War stuff where in warfare a strategic move is either a real and serious move or it is a deceptive blow.

Let's explore each character in more depth:

虚 was originally written 虛 (there is a very subtle difference in the strokes at the bottom of the character) and means unpreparedness, falsehood, emptiness, void, abstract theory, empty or unoccupied, diffident or timid, false, humble or modest, virtual, or in vain.
In the Buddhist context, 虛 represents the Pali/Sanskrit word “śūnya,” meaning empty, vacant, unreal, unsubstantial, untrue, space, humble, or in vain.
In ancient Eastern/Chinese astronomy, 虛 represents the “Emptiness” constellation (one of the 28 mansions in the sky).

実 was originally 實 in Chinese (they currently write it as 实 in Simplified Chinese) with the meaning, truth, reality, sincerity, honesty, fidelity, and substance.
The Buddhist context is similar, adding real, true, honest, really, solid, definitely, sincere, solid, fixed, full, to fill, fruit, kernel, verily, in fact, the supreme fact, or ultimate reality to the definition.