Mighty Powerful Strong in Chinese / Japanese...

強大 can mean mighty, powerful, large, formidable, or strong.

This term is often used to describe soldiers/troops/warriors and whole armies.

気の強い means strong-willed or strong of heart in Japanese.

Here's the character breakdown of this Japanese title:
気 (ki) spirit; mind; heart; nature; motivation; intention; feelings; essence.
の (no) possessive particle.
強い (tsuyoi) strong; powerful; mighty; potent; resistant; resilient; durable.

Note: Because this selection contains some special Japanese Hiragana characters, it should be written by a Japanese calligrapher.

強い体強い心 is a way to write “strong mind, strong body” in Japanese.

Each of the two lines starts with 強い (tsuyoi) which means: strong; powerful; mighty; potent; resistant; resilient; durable; tough; stiff; hard; inflexible.

The body is represented with 体 (the ancient version is 體, romanized as karada), which means: body; build; physique; posture; torso; trunk; health.

Mind is represented with 心 (kokoro), which can mean heart, mind, or soul, depending on context.

強い體強い心 is not a common phrase in Japanese, so it's not the most natural title for calligraphy. In English, you might want to write it, “strong mind, strong body” but, “strong mind, strong body,” is more natural in Japanese.

Note: Because this selection contains some special Japanese Hiragana characters, it should be written by a Japanese calligrapher.