I just spent most of the day playing this on my PSP using the emulator MasterBoy and beat it at 100%. I didn't use the rom provided here. My copy is of a rom dump of the Limited Run Games physical cartridge release of it, but the content of it is still the same. It's about a 3 and a half or so hour game. Like, short but long enough to be pretty satisfying.
This was originally free but then LRG made a physical version you could buy and now the original download for the rom was taken down. I saw where it was also released for Android too? But I don't know where to get that one. (edit: Google Play Store has it but you have to be a Crunchyroll subscriber to play it) Of course since LRG is always done in very limited copies it's not cheap to buy if you can find a copy. Like $70 to $100 or so. Which is crazy for something that was initially free.
Anyway as for the actual game it's a really good high quality aftermarket GBC release. A lot better than most of the homebrew and aftermarket games I've tried for GBC. The graphics are amazing (and if they used GB Studio for this then I have even more respect for that now) and pretty detailed for a GBC game. The cutscene stills looked impressive too. It worked surprisingly well in that older emulator on my PSP. So it's very emulation friendly.
The controls were easy to work with and felt very fluid. There wasn't a ton of different monsters but the ones it had were cute and gave enough variety and challenge for the length it had. While I know nothing about Crunchyroll-Hime and her lore, the story was nice and entertaining. It was very reliant on common anime tropes and references. The writing was silly and funny too, and I liked the personality it gave off.
Some people complained that the writing was too clichéd with the pop culture references and jokes, but obviously that's the whole entire point of the game due to what it's based on. They're idiots for thinking that can be seen as a negative to it. One of my favorite parts was one of the cultural references:
The horror mangaka Junji Itō is a supporting character in the game and lives in New Crunchy City. You have to help him find his lost cat in order to get the key to the Underlord's Crypt (Junji Itō is well known as a cat lover and has a whole manga series about his real life cats). Just that alone was very endearing to me since I'm a fan of Junji Itō and have read most of all his manga.
The level of difficulty is pretty well balanced I think. The regular enemies mostly take 3 or 4 hits with the sword to kill and the bosses are tame compared to most action rpgs but aren't without challenge. For a harder challenge you can find the Cursed Amulet item and it'll unlock a harder new game+ mode. To get the item you need to do the puzzle that unlocks the Underlord's boss door using the Konami code instead (up, up, down, down, left, right, left, right) then after saving the game and restarting press select on the load file screen to be able to start a file in the harder cursed mode.
There's 10 hidden health upgrades in total for a max of 14 health. Each of the shops have one on sale, but you have to find the rest. The weapons are all bought in the store too, but the Shrine Maiden npc will give you the bow for the arrows you can buy. The boomerang is 400 yenny and not really worth the grinding for money unless you're a completionist. Every square in the pause menu has an item. So when you have them all full, 14 health, 16 bombs, 32 arrows, and all weapons before going against the last boss then you have 100% completion.
All in all if you like Zelda-ish games then I'd highly recommend taking the time to play this one. My only singular complaint is that I didn't like the music that much and it was almost bordering on annoying sometimes, but that's just me. Maybe you guys might like the soundtrack more? It left me feeling pretty satisfied when I reached the Thanks for playing screen at the end (there was even a cute little what the characters are up to now thing after) and I didn't feel like my time was wasted. A solid 8 or 9 out of 10. Possibly a 10 if I had really liked the chiptune soundtrack instead.
There's an official walkthrough
here, but it doesn't help with finding the health upgrades.