Might as well start calling them by their new name. If you haven't noticed Kousei Gakuin (光星学院) changed their name to Hachinohe Gakuin Kousei (八戸学院光星) or in shorthand Kousei (光星).
No matter what you call it, their rise to prominence has been sudden. There were signs when they went to Natsu Kousien 3 of 4 years in 2000-2003 reaching the quarterfinals twice and the semifinals the other time. But in 2011 they stamped their mark in history (albeit infamously), by reaching 3 straight calendar Koushien finals losing all of them.
The school went through the name change right afterwards and while they haven't had the same success (it's hard not to unless they actually won the whole thing), but after a full year off went to Koushien both times in 2014, and senbatsu in 2015.
And here they are again. They've done it defeating every team they should have soundly, and winning the close games against the upper tier teams (except for the Aomori Yamada rematch in the finals). They did it leaning on ace Sakurai Kazuki (桜井 一樹). I don't have much information on him other than possibly having a slider, curve and changeup. That, and the fact that he doesn't strikeout many batters can be a concern if he doesn't have pinpoint control.
Offensively, it's hard to identify a person who stands out. Perhaps the top of the order which naturally should have your better hitters. But then you turn to their loss against Aomori Yamada, and they could muster just 3 hits. If the pitching is very contact-dependent, the offense will need to come though in case Sakurai doesn't have his best.