(Though in the end Yaeyama will probably get the bid - but that article will come later)
Kaisei, seemed to fall short in both attempts to win their taikais. First was the Shimane prefecturals where Taisha routed them 12-0 (though that could also be because they already qualified), then were shutout again in the semifinals against Soushi Gakuen in the super-regionals. But they were also able to beat Izumo twice (beating a team twice is never easy), held on to defeat Risshoudai Shounan, as well as shutting out Hiroshima Shinjyou.
Kaisei rides on ace Yoshikawa Takahiro (吉川 貴大), who reportedly can hit the low 140s, but probably lies in the upper 130s at best, with a slider/forkball combo. He only went 18K/10BB in his 25 innings of work during the super-regionals.
Offensively, there is literally no batter who stands out, everyone seems equally capable of getting a base hit, with perhaps the exception of RF Hosoda Yuuta. It's just that everyone is also average as well - which may mean no black holes in the lineup (good), but nobody to be scared about (bad).
So, with average pitching and average hitting, you have an average team - which just won't fly at Koushien. Here's your participation medal, thanks for playing.