Takeru is really scared to get a ride on the back of his motorcycle, but he answerd to him that "I am scared" with panache (he looks like unscared).「でかい図体」means hulking. I hope this May help u

Image big pro wrestler stand in fornt of you and He is little uncomfortable feeling and　look down you this is vision which you feel form this sentence . でかいずうたい＝　大きなからだ（big man ) 怖いからだ　＝this case he might have many scar and well trained body 堂々＝nothing fear . this case meet night dark steet meet with big scared pro wrestler and look at you and you scared I can image this case