Near the end of the game, he found the location of the WWW Research Facility. Yuichiro also reveals that Lan and MegaMan are brothers.
Dr. Hikari was taken into the Seaside Hospital after overworking himself. He gives Lan the Navi Customizer, and before Lan goes to Castle Wily, he gives him the NaviCust program "Alpha", which allows MegaMan to see hidden parts of Alpha in the Cyberworld. Later on, he manages to decipher Tadashi Hikari's note given by Lan after Lan and Hub meet Tadashi inside the remains of Alpha. On the finale, he managed to brought MegaMan.EXE back to life with the deciphered note from his father.
Yuichiro takes a more prominent role in the asteroid crisis. He works with the other scientists to develop the Red Sun/Blue Moon Laser. While busy, at one point he returns the NaviCust to Lan, which Haruka had taken away from him. Later when Dr. Regal is about to send LaserMan to Duo's asteroid, he confronts Dr. Regal, discovering that he is the leader of Nebula, but when Lan arrives, Dr. Regal ambushes him and knocks out Yuichiro.
Yuichiro is kidnapped by Nebula in order for them to find out where Gow is. Yuichiro doesn't tell them, but they catch Gow anyway. He is rescued by Team ProtoMan/Team Colonel, but remains behind after Nebula Grey is defeated to encourage Dr. Regal to turn his back on evil, telling him that he still has faith in him before fainting. He and Dr. Regal are rescued by Baryl.
Yuichiro has to move to Cyber City to work on a new project with the Central Town mayor, Cain. During first encounter with Cybeasts, Yuchiro warns Lan and Mega Man not to use program that he installed inside Mega Man that causes Hub to seal Cybeast inside him. Later after contained and stabilize, he gave Mega Man guide about to utilize Cybeast power. Yuichiro is later framed and arrested at Green Town by Prosecutor Ito. After the battle with the Cybeasts, he and his family return to ACDC Town.
In the anime, he doesn't appear very often in the beginning of the series. But, he gives Lan a package which transforms his NormalNavi into MegaMan. Later, he stays at SciLab and performs various research tasks, and assists Lan and the Cross Fusion Members.
Hikari means "light" in Japanese.