DASS-393 _The father who left home suddenly returned to visit the mother and child

Nagai Maria is a single mother. She gave birth to the child Ichika and raised him alone. Now, Ichika has grown up. She wanted to know who her biological father was, so after many efforts, today Ichika was able to meet him. The father and son talked for a long time, and they even took photos as souvenirs. When returning home, a strange man said he wanted to meet Nagai. Ichika inquired and he claimed to be her father. In the end, who is Ichika's biological father? What truth is being hidden after 17 years?