Hitorigurashi, Netsu wo Dasu. Koi wo Shiru.

The protagonist caught a cold over Christmas, took the day off from work, and was laid up alone in bed. Then an unknown blonde gal showed up to take care of him. "Uhh... who?" he wondered, but being in the worst physical health, he ended up letting her take care of him...

(Source: Kadokawa, translated)