He has studied the theory of money, macro dynamics, evolutionary economics, philosophy of corporations, fiduciary law, and the history of sociology.

He has also written books and articles in newspapers and magazines for the general public on a wide variety of subjects ranging from global capitalism, post-modernity, civil society, money and language to literature and movies.

His keen observations and analysis of the works of Shakespeare, Marx, J. S. G. Boggs, and Ihara Saikaku have established him as one of the foremost essayists in Japan.

He has then argued in opposition to the neoclassical view of the self-regulating nature of laissez-faire market mechanism, that what stabilizes the monetary economy is the inflexibility of money wages and that an equilibrium it gravitates to almost never achieves full-employment.

He has offered proof, in his search-theoretic model of decentralized exchanges, that, to sustain itself as an equilibrium, the monetary system requires no "real" conditions.

Iwai is credited with constructing mathematical models of Schumpeterian evolutionary processes that describe how large numbers of firms interact with one another, by competing to innovate, trying to imitate and struggling to grow.