Yukkuraium is a game where you take care of yukkuri in a small aquarium. Also once you reach level 4 or 5 you can slice the yukkuri into two,
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There are more recent versions. The most recent ones have kos and different types(these are usually just sprite changes so it's not much different). From the types, there's Marisa, Reimu, Alice, Patchouli, and YuukaChen. The kos seem to only be Marisa and Reimu, though. Also, most recently, you can take off the hats off all types There are a couple versions that are translated, so you can see what the little things are saying.
English Translations can be found here: https://groups.google.com/forum/#!topic/yufanfics/3I63A2i_g5U