Touhou's fall run was anything but easy. Of their 10 games they played, 7 of which were decided by 2 runs or less (the other 3 were mercy-rule blowouts). But they avoided all the dangerous teams in Aichi, before finally facing top-level competition in the super-regionals - though to be fair, it was mainly against 2 schools from Mie (Mie, Inabe Sougou Gakuen). Still, they won the title and narrowly lost to Aomori Yamada in the quarterfinals.
Ace Fujishima Kento (藤嶋 健人) appears to be where the buck stops. He pitched every inning but in the first game of their run. Since Touhou was at Natsu Koushien, we have a good idea of what he can do. He can throw in the low-140s, the delivery looks very quick and the ball can sneak up on a batter, much like that grounder in the 1st AB of that video. It can also explain the high K rates during the tournament (he did have an abbreviated 7 inning no hitter against Chuukyou in the super-regionals). But it looks like under the spotlight it's not as effective - though after a run at Koushien he may have tightened his game up. With no one behind him, it's him or bust.
What's troubling - and that may have been expected due to their low offense, is that one of their best hitters... is Fujishima. Now, there are strong teams that have their ace as their best offensive player - just ask Tsuruga Kehi. But it's more likely that the ace as a cleanup hitter means that the offense is fairly weak. Yes, there is leadoff hitter LF Suzuki Mizuki (鈴木 光稀) and 1B Matsumoto Ryuuya (松本 凌弥), but I'm not sure if that will be enough to carry the team - but they certainly can hang in there if Fujishima can hold up.