Anata to Senya Ichiya(2000)

Anata to Senya Ichiya

Ooizumi Sonoko is the most efficient office lady in her company and she doesn't have time for men. However, one night she gets drunk and when she wakes up next morning, she finds the man of her dreams on the bed with her. That was supposed to be one night's love, but she finds out that he's her new section chief!

This series was published as part of vol 2 - 5 in Oboretai and the first 3 chapters can be found in vol 2.