Tsumugu: Our Ray of Light

Koharu is a single mother living with her 5-year-old son, Tsumugu. Her days are busy and never dull. But Koharu has one thing she's been keeping to herself... She hasn't told Tsumugu where his father is. But then one day, the wheels of fate begin to turn. Koharu randomly encounters her ex, a firefighter named Gaku. And Gaku is Tsumugu's biological father. Due to things that happened in the past, Koharu disappeared from Gaku's life without a word when she got pregnant. She thought they would never meet again, but here they are, face to face. Gaku tells Koharu that he's been searching for her all this time, his gaze focused on the future, not the past. Unaware that Gaku is his father, Tsumugu innocently opens his heart to him. This puts a knot in Koharu's chest. Koharu wanted to protect Tsumugu, but was the choice she made the right one? The truth she hid, and her feelings are being woven anew... The relationship between the three begins to change, as if to make up for the lost time...

(Source: MangaPlaza)