Manga - the weak MC runs away from his lover... he lives in the wild and becomes strong

Question

I am looking for a manga (it's not "level up by eating").

The MC is a young man. He's in love with his childhood friend. She was in the hero's party. When she came back from her adventure, the MC sees her next to the hero and he thinks his friend and the hero are in love (it's a mistake) Well.. he's extremely sad, so, he runs away. He goes to a forest or mountain... He lives there alone... he eats what he can eat to survive... a lot of strange food... he's sick, but each times, he grows stronger and stronger. At some point, he's not a human anymore.

Others things :

• his sister is looking for him
• there is a dragon in the story (later)

It's something I read on a website so it's probably a manga (Japanese translated in English). I don't think it was a manhwa (Korean comic) but maybe I am wrong.

Answer 1

I am fairly sure this sounds exactly like Sono Mono Nochi Ni… (WN) It appears it was rebooted though. (from Sono Mono. Nochi ni... to Sono Mono. Nochi ni... (NARIIE Shinichirou)

Pretty sure this is exactly what you are looking for. However, from what I can tell anyways, the mistake is not a mistake. Might be wrong on that though.

99.99% sure this is it though. Enjoy either way.

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Description of Works / Preservation Data

[First Link:]

• Site "novelupdates.com" is an info listing of thousands of light novels. If it's been published officially then it is most likely listed on this site. (fan novels, or wip things on forums are typically not included)
• The novel of "Sono Mono Nichi ni" (this is also the source the manga draws upon.)
• It follows Wazu, who was an ordinary townsman. (The Main Character, and the Protagonist)

• He's in love with someone, they promise to marry while children. Later on his love returns but she is now fated to marry someone else. Wazu takes this terribly and runs away from his life to live in mountains for two years. During these years typical light novel tropes such as eating mysterious things that increase the protaganists power occur. Eventually he can basically one-hit KO a dragon.

[Second Link:]

• This is the initial manga adaptation of the novel. It was serialized in Comic Earth Star (magazine) and published originally by Earth Star Entertainment. Art by AYANO Urasuke. Supposedly one volume was completed before it was dropped. This follows the same story as the novel.

[Third Link:]

• Site "mangaupdates.com" is basically a wiki of manga and their various fan translations.
• This is the rebooted manga adaptation. Published and serialized by the same entities as the first iteration. Art now done by NARIIE Shinichirou.
• The current manga reboot. It, also, follows the story of the novel.
• twenty-four chapters have been fan-translated as of now.
• 4 volumes are completed in original language and ongoing.