Kanna (2002)

Kagura Sagaki is an average, hard-working guy who thought that his biggest problem in life was paying the bills. That is, until the day he woke up with a young girl curled up in his futon. Kanna can’t even speak, and when she tries to communicate by written word, the language is completely alien to him. Kagura is baffled as to why and how she showed up in his apartment. But when he goes to work and finds his boss has murdered everyone in sight, he begins to suspect not all is ordinary - especially when his body is taken over by another’s spirit and used to defeat his former employer. Kagura must journey on foot with his new companion to seek out Mikoto, the childhood friend he left behind... and answers to the deepening mystery of Kanna.

Source: www.anisearch.com/manga/3224