Mion chapter are manga redraws with coloring i did when game was made over a decade a go. When you get to chapters that never got offical english translation or unique there will be less anime images.
The game is more closely to manga and the vn than the anime. This game takes place in timeframe of kai (2nd season), but as you finish chapters, you find the first season of the anime reflected by a different method, you see orbs rather than kakera to click for these. Finishing chapters unlock new content plus different treasures in all chapters including the freeplay sandbox where you find rarer stuff and new character unlocks. There also different endings to chapters that effect the rest of the game.
If you started with the rika puzzle chapter, it quickest way to other chapters by quickly having a bad end. Someone who seen higu will realize a bad end will be coming if they pick the Rika choice. Rika chapter does not stop at Mion's minigame though, if you either super lucky or figure out how to beat mion, there are still more puzzles. If you are hard up figuring the next one which most people do, you can return with x-ray specs to cheat, as rika would likely cheat ;)
If you need help or hints, i will be here. There is a lot in this game.
You can find that kenta-kun, though it will be like 1 out 100 odds per dig, plus its a nice prize if you are lucky.
