The text on the guy's shirt is a Japanese proverb: Fuurinkazan (lit. wind, forest, fire, mountain), which means "as fast as the wind, as quiet as the forest, as daring as fire, and immovable as the mountain".
The girl's shirt is similarly a Japanese proverb: Yuigadokuson, although the meaning is nowhere as profound since it means "I'm the greatest" or "No one in this world is more exalted/noble than me."
風林火山 was Shingen Takeda's war motto or something similar. IIRC it's like the Japanese port of the same thing said by Sun Tzu.
Can't remember exactly but I think 唯我独尊 had origin from Buddhism.