This year corresponds to AD 2024, also known as AC5. Now, what does AC stand for? That’s right, it’s short for After Corona. The first year of AC, AC1, began in AD 2020, the year when COVID-19 emerged, and the years before that are referred to as BC (Before Corona)(). As many of you have experienced, lifestyles have drastically changed since AC1. For example, I consider remote working to be a major shift comparable to the Industrial Revolution in the late 18th century. Although I proposed BC and AC as concepts to replace BC (Before Christ) and AD (Anno Domini) in my ‘tweets,’ it did not catch on widely. This year, I hope that you, the readers of these tweets, and our research lab can propose innovative concepts that will be remembered for generations to come. Furthermore, I pray that AC5 will be a wonderful year for all of you. () Fujii, ‘Proposing a New B.C. and A.C.’, January 2022.”