True Real Sincere 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

屋烏の愛 is a Japanese way to express true love or deep love.

The phrase literally suggests that this is a love for someone so strong that it can reach a crow perched on that person's roof.

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.