Well I will say one to other people not wanting spoilers that they shouldn't read this reply.
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It ends with Anzhe sacrificing himself for all the humanity as he is anyway dying. Anzhe is a little mushroom, their life span is 3 months and only purpose is to create a spore, as u already know from the manga he treats it as "his while life"... and it's literally as we get to know after Anzhe sacrifice himself. The mushroom was his orginal body that was damaged, he broke and wanted to live so bad that he created a spore, that spore was his new body growing. At that time he didn't know it, he only thought that his spore is like any spore of the mushrooms, "every muchroom dies after the spore leaves it" or something like that and the spore creates a new mushrooms and it continues a cycle. I don't want to explain mushrooms reproduction, as it is chaotic already haha. So at some point in the novel Anzhe left the spore with judge, as the spore didn't wanted to left judge even when Anzhe told it that it isn't safe. A lot of shit happends in world, Anzhe sacrifice his "shell", world is now stable. Then we have time skip to 3 years later and we get to know that judge and one doc nutured the spore anzhe left. The spore grow into an body and Anzhe had his memories and it explained then all with the spore thing and why it was like it was... well novel explains it better than I do.... sorry for the chaos, I'm still excited from reading it hahah
I read it there: https://www.novelhall.com/little-mushroom-21511/
Come back from finishing the novel, I'm in love with this story so I'm happy that after novel I can cope with ending it while reading this adaptation.