“𝑰 𝒘𝒂𝒏𝒕 𝒕𝒐 𝒅𝒊𝒆. 𝑰 𝒎𝒖𝒔𝒕 𝒅𝒊𝒆. 𝑳𝒊𝒗𝒊𝒏𝒈 𝒊𝒕𝒔𝒆𝒍𝒇 𝒊𝒔 𝒕𝒉𝒆 𝒔𝒐𝒖𝒓𝒄𝒆 𝒐𝒇 𝒔𝒊𝒏.” 

Depressing ngl. I could see the nihilistic ideology & undertones in the book. How Yozo see's his life and people around him and his subsequent downfall in life is extremely depressing. Yozo goes through abuse in childhood and i think that's what subsequently numbs him to life but it's indicated that he had already somehow developed a nihilistic approach to life and it seems his parents especially his father neglected him. And then growing up he lives in a facade, he doesn't let people see his true nature because he's afraid of them. He loathes life and then when probably for the 1st time he falls in love with someone, she dies.

"𝙎𝙝𝙚 𝙙𝙞𝙚𝙙. 𝙄 𝙬𝙖𝙨 𝙨𝙖𝙫𝙚𝙙."

After this incident, he probably goes into a guilt trip and eventually his addiction to alcohol just increases. Then with some hope he marries Yoshiko and makes some progress but then the incident with Yoshiko pushes him back again.That scene is somehow confusing, because Yozo somehow implies that Yoshiko was sexually assaulted but then on other instances he implies she cheated on him. This also makes him an unreliable narrator.
And finally he falls into drug addiction and finally he goes to rehab, leaves Tokyo and lives in countryside and the novel ends

“𝑵𝒐𝒘 𝑰 𝒉𝒂𝒗𝒆 𝒏𝒆𝒊𝒕𝒉𝒆𝒓 𝒉𝒂𝒑𝒑𝒊𝒏𝒆𝒔𝒔 𝒏𝒐𝒓 𝒖𝒏𝒉𝒂𝒑𝒑𝒊𝒏𝒆𝒔𝒔. 𝑬𝒗𝒆𝒓𝒚𝒕𝒉𝒊𝒏𝒈 𝒑𝒂𝒔𝒔𝒆𝒔.”

“𝑻𝒉𝒂𝒕 𝒊𝒔 𝒕𝒉𝒆 𝒐𝒏𝒆 𝒂𝒏𝒅 𝒐𝒏𝒍𝒚 𝒕𝒉𝒊𝒏𝒈 𝑰 𝒉𝒂𝒗𝒆 𝒕𝒉𝒐𝒖𝒈𝒉𝒕 𝒓𝒆𝒔𝒆𝒎𝒃𝒍𝒆𝒅 𝒂 𝒕𝒓𝒖𝒕𝒉 𝒊𝒏 𝒕𝒉𝒆 𝒔𝒐𝒄𝒊𝒆𝒕𝒚 𝒐𝒇 𝒉𝒖𝒎𝒂𝒏 𝒃𝒆𝒊𝒏𝒈𝒔 𝒘𝒉𝒆𝒓𝒆 𝑰 𝒉𝒂𝒗𝒆 𝒅𝒘𝒆𝒍𝒍𝒆𝒅 𝒖𝒑 𝒕𝒐 𝒏𝒐𝒘 𝒂𝒔 𝒊𝒏 𝒂 𝒃𝒖𝒓𝒏𝒊𝒏𝒈 𝒉𝒆𝒍𝒍. 𝑬𝒗𝒆𝒓𝒚𝒕𝒉𝒊𝒏𝒈 𝒑𝒂𝒔𝒔𝒆𝒔” 

 “𝑰 𝒔𝒖𝒑𝒑𝒐𝒔𝒆 𝒊𝒕 𝒘𝒐𝒖𝒍𝒅 𝒃𝒆 𝒏𝒐 𝒆𝒙𝒂𝒈𝒈𝒆𝒓𝒂𝒕𝒊𝒐𝒏 𝒕𝒐 𝒔𝒂𝒚 𝒕𝒉𝒂𝒕 𝒕𝒉𝒆 𝒘𝒐𝒓𝒍𝒅 𝒊𝒔 𝒄𝒐𝒎𝒑𝒐𝒔𝒆𝒅 𝒆𝒏𝒕𝒊𝒓𝒆𝒍𝒚 𝒐𝒇 𝒖𝒏𝒉𝒂𝒑𝒑𝒚 𝒑𝒆𝒐𝒑𝒍𝒆”

Throughout the novel Yozo acts like helpless and pessimistic person. He shows almost no emotions whatsoever and ends up ruining his life. 

“𝑫𝒊𝒔𝒒𝒖𝒂𝒍𝒊𝒇𝒊𝒆𝒅 𝒂𝒔 𝒂 𝒉𝒖𝒎𝒂𝒏 𝒃𝒆𝒊𝒏𝒈. 𝑰 𝒉𝒂𝒅 𝒏𝒐𝒘 𝒄𝒆𝒂𝒔𝒆𝒅 𝒖𝒕𝒕𝒆𝒓𝒍𝒚 𝒕𝒐 𝒃𝒆 𝒂 𝒉𝒖𝒎𝒂𝒏 𝒃𝒆𝒊𝒏𝒈.”

There is a reference to Crime and Punishment by Dostoevsky in the book where Yozo is trying to find antonym for crime:

“𝘈𝘤𝘵𝘪𝘰𝘯𝘴 𝘱𝘶𝘯𝘪𝘴𝘩𝘢𝘣𝘭𝘦 𝘣𝘺 𝘫𝘢𝘪𝘭 𝘴𝘦𝘯𝘵𝘦𝘯𝘤𝘦𝘴 𝘢𝘳𝘦 𝘯𝘰𝘵 𝘵𝘩𝘦 𝘰𝘯𝘭𝘺 𝘤𝘳𝘪𝘮𝘦𝘴. 𝘐𝘧 𝘸𝘦 𝘬𝘯𝘦𝘸 𝘵𝘩𝘦 𝘢𝘯𝘵𝘰𝘯𝘺𝘮 𝘰𝘧 𝘤𝘳𝘪𝘮𝘦, 𝘐 𝘵𝘩𝘪𝘯𝘬 𝘸𝘦 𝘸𝘰𝘶𝘭𝘥 𝘬𝘯𝘰𝘸 𝘪𝘵𝘴 𝘵𝘳𝘶𝘦 𝘯𝘢𝘵𝘶𝘳𝘦. 𝘎𝘰𝘥 . . . 𝘴𝘢𝘭𝘷𝘢𝘵𝘪𝘰𝘯 . . . 𝘭𝘰𝘷𝘦 . . . 𝘭𝘪𝘨𝘩𝘵. 𝘉𝘶𝘵 𝘧𝘰𝘳 𝘎𝘰𝘥 𝘵𝘩𝘦𝘳𝘦 𝘪𝘴 𝘵𝘩𝘦 𝘢𝘯𝘵𝘰𝘯𝘺𝘮 𝘚𝘢𝘵𝘢𝘯, 𝘧𝘰𝘳 𝘴𝘢𝘭𝘷𝘢𝘵𝘪𝘰𝘯 𝘵𝘩𝘦𝘳𝘦 𝘪𝘴 𝘱𝘦𝘳𝘥𝘪𝘵𝘪𝘰𝘯, 𝘧𝘰𝘳 𝘭𝘰𝘷𝘦 𝘵𝘩𝘦𝘳𝘦 𝘪𝘴 𝘩𝘢𝘵𝘦, 𝘧𝘰𝘳 𝘭𝘪𝘨𝘩𝘵 𝘵𝘩𝘦𝘳𝘦 𝘪𝘴 𝘥𝘢𝘳𝘬𝘯𝘦𝘴𝘴, 𝘧𝘰𝘳 𝘨𝘰𝘰𝘥, 𝘦𝘷𝘪𝘭. 𝘊𝘳𝘪𝘮𝘦 𝘢𝘯𝘥 𝘱𝘳𝘢𝘺𝘦𝘳? 𝘊𝘳𝘪𝘮𝘦 𝘢𝘯𝘥 𝘳𝘦𝘱𝘦𝘯𝘵𝘢𝘯𝘤𝘦? 𝘊𝘳𝘪𝘮𝘦 𝘢𝘯𝘥 𝘤𝘰𝘯𝘧𝘦𝘴𝘴𝘪𝘰𝘯? 𝘊𝘳𝘪𝘮𝘦 𝘢𝘯𝘥 . . . 𝘯𝘰, 𝘵𝘩𝘦𝘺'𝘳𝘦 𝘢𝘭𝘭 𝘴𝘺𝘯𝘰𝘯𝘺𝘮𝘰𝘶𝘴. 𝘞𝘩𝘢𝘵 𝘪𝘴 𝘵𝘩𝘦 𝘰𝘱𝘱𝘰𝘴𝘪𝘵𝘦 𝘰𝘧 𝘤𝘳𝘪𝘮𝘦? 𝘊𝘳𝘪𝘮𝘦 𝘢𝘯𝘥 𝘱𝘶𝘯𝘪𝘴𝘩𝘮𝘦𝘯𝘵. 𝘋𝘰𝘴𝘵𝘰𝘪𝘦𝘷𝘴𝘬𝘪. 𝘛𝘩𝘦𝘴𝘦 𝘸𝘰𝘳𝘥𝘴 𝘨𝘳𝘢𝘻𝘦𝘥 𝘰𝘷𝘦𝘳 𝘢 𝘤𝘰𝘳𝘯𝘦𝘳 𝘰𝘧 𝘮𝘺 𝘮𝘪𝘯𝘥, 𝘴𝘵𝘢𝘳𝘵𝘭𝘪𝘯𝘨 𝘮𝘦. 𝘑𝘶𝘴𝘵 𝘴𝘶𝘱𝘱𝘰𝘴𝘪𝘯𝘨 𝘋𝘰𝘴𝘵𝘰𝘪𝘦𝘷𝘴𝘬𝘪 𝘳𝘢𝘯𝘨𝘦𝘥 '𝘤𝘳𝘪𝘮𝘦' 𝘢𝘯𝘥 '𝘱𝘶𝘯𝘪𝘴𝘩𝘮𝘦𝘯𝘵' 𝘴𝘪𝘥𝘦 𝘣𝘺 𝘴𝘪𝘥𝘦 𝘯𝘰𝘵 𝘢𝘴 𝘴𝘺𝘯𝘰𝘯𝘺𝘮𝘴 𝘣𝘶𝘵 𝘢𝘴 𝘢𝘯𝘵𝘰𝘯𝘺𝘮𝘴. 𝘊𝘳𝘪𝘮𝘦 𝘢𝘯𝘥 𝘱𝘶𝘯𝘪𝘴𝘩𝘮𝘦𝘯𝘵—𝘢𝘣𝘴𝘰𝘭𝘶𝘵𝘦𝘭𝘺 𝘪𝘯𝘤𝘰𝘮𝘱𝘢𝘵𝘪𝘣𝘭𝘦 𝘪𝘥𝘦𝘢𝘴, 𝘪𝘳𝘳𝘦𝘤𝘰𝘯𝘤𝘪𝘭𝘢𝘣𝘭𝘦 𝘢𝘴 𝘰𝘪𝘭 𝘢𝘯𝘥 𝘸𝘢𝘵𝘦𝘳. 𝘐 𝘧𝘦𝘭𝘵 𝘐 𝘸𝘢𝘴 𝘣𝘦𝘨𝘪𝘯𝘯𝘪𝘯𝘨 𝘵𝘰 𝘶𝘯𝘥𝘦𝘳𝘴𝘵𝘢𝘯𝘥 𝘸𝘩𝘢𝘵 𝘭𝘢𝘺 𝘢𝘵 𝘵𝘩𝘦 𝘣𝘰𝘵𝘵𝘰𝘮 𝘰𝘧 𝘵𝘩𝘦 𝘴𝘤𝘶𝘮- 𝘤𝘰𝘷𝘦𝘳𝘦𝘥, 𝘵𝘶𝘳𝘣𝘪𝘥 𝘱𝘰𝘯𝘥, 𝘵𝘩𝘢𝘵 𝘤𝘩𝘢𝘰𝘴 𝘰𝘧 𝘋𝘰𝘴𝘵𝘰𝘪𝘦𝘷𝘴𝘬𝘪'𝘴 𝘮𝘪𝘯𝘥—𝘯𝘰, 𝘐 𝘴𝘵𝘪𝘭𝘭 𝘥𝘪𝘥𝘯'𝘵 𝘲𝘶𝘪𝘵𝘦 𝘴𝘦𝘦 . . . 𝘚𝘶𝘤𝘩 𝘵𝘩𝘰𝘶𝘨𝘩𝘵𝘴 𝘸𝘦𝘳𝘦 𝘧𝘭𝘢𝘴𝘩𝘪𝘯𝘨 𝘵𝘩𝘳𝘰𝘶𝘨𝘩 𝘮𝘺 𝘩𝘦𝘢𝘥 𝘭𝘪𝘬𝘦 𝘢 𝘳𝘦𝘷𝘰𝘭𝘷𝘪𝘯𝘨 𝘭𝘢𝘯𝘵𝘦𝘳𝘯 𝘸𝘩𝘦𝘯 𝘐 𝘩𝘦𝘢𝘳𝘥 𝘢 𝘷𝘰𝘪𝘤𝘦.”