The European heavyweights meet in the last four in Durban on Wednesday in an eagerly-awaited repeat of the Euro 2008 final which Spain won 1-0 with a goal from Fernando Torres.
Coach Vicente del Bosque's side is little changed, while his German counterpart Joachim Low has selected the country's youngest squad since 1934, blending an exciting crop of new talent with experienced campaigners.
"They are perhaps the most complete team at the World Cup, one that has been overhauled since the 2008 final with young and fresh faces," Reina said at a news conference at Spain's training base in Potchefstroom.
"It's going to be tough as they are the strongest opponent right now but we believe in ourselves," he added.
Spain, who are bidding for a first World Cup triumph, have struggled at times in South Africa against defensive-minded opponents who try to prevent them from asserting their customary dominance of possession.
However, Germany have been deploying similar tactics to the Spanish based around rapid passing, movement off the ball and devastating counter-attacking, raising the prospect of an open, free-flowing game.
"Maybe we play the ball around more and they are more direct but I don't think we are very different," Reina said. "We have to make sure they don't get a lead because they are a very difficult team."
After a shock 1-0 defeat to Switzerland in their opening Group H match, Spain's progress to the last four has been much trickier than expected and the poor form of Torres, who plays with Reina at Liverpool, has been a major concern.
Torres returned from knee surgery shortly before the tournament and has yet to find the net in five matches, while his strike partner David Villa is the tournament's leading scorer with five.
"He (Torres) is a very mature person and he knows perfectly well that this is what happens sometimes in football and he has to stay calm," Reina said.
"He has the confidence of the coach, of his team mates and of himself. Hopefully he'll make history again like at Euro 2008 and be a key player for us."
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