He was an elderly man who was truly kind and a brilliant scientist, though tragically, he never got to live long enough to see the birth of his grandsons, but he would be very proud of them. Lan still loves his grandfather and wished that he would have just lived a little longer to be with him.
Tadashi first appears after Alpha is defeated. There is a strange door left over which MegaMan and Lan go into. Inside is the saved memories and persona of Tadashi. He talks to Lan about Alpha's origins and also about personal things such as the family. Lan wants him to escape with them, but he can't because he only exists in Alpha. The hologram disappears eventually because Alpha was destroyed.
He appears in flashbacks which show him working with Lord Wily on SoulNet with the intention of bringing peace to the world. It is shown that while they did extensive research, they decided to leave it up to their descendants to finish. During the final battle with Nebula Grey, Tadashi's voice seems to reach Lan through SoulNet and encourages him to win. This gives Lan the strength to fight SoulNet and Nebula Grey.
In episode 15, it is revealed that, in his youth, he created the Net Wrecker, a device which can boost a NetNavi's power to epic proportions. He later exchanged the Wrecker for some ramen. Curiously, the Net Wrecker works with the Advanced PET, invented immediately prior to the events of Axess, years after Dr. Hikari died.
In the Rockman.EXE Stream movie, an evil program is named after him, and he is seen in a flashback.
A hologram of the Beyondard version of Hikari Tadashi appeared in Episode 20 of Beast. He talked about how Beyondard came into existence, how Dr. Wily of Beyondard, now but a conscious stored within an Android Brain, created the Beast Factor, and how Iris was created. He also created the Synchronizer, Trill, in order to win the war against the Zoanoroids.
- Hikari (光) means Light and Tadashi (正) can mean Right, both similar to the name of his original counterpart, who is referred to as Dr. Light and Dr. Right.
- It is unknown if his original counterpart have a biological son and grandsons. It is unknown if the original Dr.Light have biological descendants.