Japan also does not allow its adult citizens to have other nationalities. Those who have Japanese and another nationality from birth are required to choose one after reaching adulthood or risk losing their Japanese nationality [1]. Those acquiring Japanese nationality are also required to renounce other nationalities if possible [2, Article 5].

I know someone who was born in the Soviet Union and, after living in Japan for many years, became a Japanese citizen. She had problems renouncing her previous citizenship because the country where she was born no longer existed; she said she had to bribe someone at the Russian Embassy to get the necessary documentation. She also mentioned being detained and questioned when trying to enter Canada on her Japanese passport for a short stay because the Canadian immigration officials thought she didn’t look Japanese. She had no similar difficulties when trying to enter Japan itself.

[1] http://www.moj.go.jp/ENGLISH/information/tcon-01.html

[2] http://www.moj.go.jp/ENGLISH/information/tnl-01.html

That’s easily “circumvented” with an OCI (Overseas Citizenship of India) card. You lose the right to vote or hold public office, but have permanent residence and authorisation to work.

Yes, but India has something called Person Of Indian Origin Card, PIO Card. Which is also known as semi passport. You don't need visa to Infia, can buy land, business. Cant vote, stand in elections, hold government jobs.

Edit: or i think its OCI Card, Overseas Citizen of India. PIO is discontinued.

Check out the fines. It can (and is) done by a lot of people.

If you were ok with settling outside India you could become a citizen of another country which supports dual citizenship.