Kayashimashi no Yuuga na Seikatsu

By Backlash67:

This series follows the life of Sumito Kayashima. Sumito is a spoiled, wealthy yet lazy young man. Sumito doesn't work. He spends his days going to parties and frivilously spending away his wealth on antiques, books he doesn't intend to read, and other such things. His daily routine and interests are managed by his hired conversationalist/secretary Koizumi.

Sumito seems to be the quite, naive little rich boy but when night comes his innocent mask comes off to reveal a much more conniving and wanton man.