He didn't see a 'person' in their first reincarnation, he saw the prince. He didn't see hikaru as a master when he was a dog, he thought of him as his prince he needed to protect. Even when he became a grandpa to Hikaru, he never saw him as his grandson, he saw him as the prince yet again. He never treated hikaru as his grandson, and never actually considered him as one, Takao only focused on the fact that his 'grandson' was the reincarnation of his prince.
By that fact, Takao unconsciously disregarded the identity of Hikaru in each reincarnation. Hence why he was able to date his former grandson, because he never actual treated hikaru as one.
In each of Hikaru's reincarnation, Takao only thought of him as the Finley, not anything else. This might be the first reincarnation where Takao was slightly able to differentiate Hikaru from Prince Finley. Hikaru pretended he didn't remember because he knew Takao had such habit of only looking at him as Finley nothing else. So Hikaru wanted a relationship with Takao simply as Takao and Hikaru, not as Prince and Knight.
He didn't see a 'person' in their first reincarnation, he saw the prince. He didn't see hikaru as a master when he was a dog, he thought of him as his prince he needed to protect. Even when he became a grandpa to Hikaru, he never saw him as his grandson, he saw him as the prince yet again. He never treated hikaru as his grandson, and never actually considered him as one, Takao only focused on the fact that his 'grandson' was the reincarnation of his prince.
By that fact, Takao unconsciously disregarded the identity of Hikaru in each reincarnation. Hence why he was able to date his former grandson, because he never actual treated hikaru as one.
In each of Hikaru's reincarnation, Takao only thought of him as the Finley, not anything else. This might be the first reincarnation where Takao was slightly able to differentiate Hikaru from Prince Finley. Hikaru pretended he didn't remember because he knew Takao had such habit of only looking at him as Finley nothing else. So Hikaru wanted a relationship with Takao simply as Takao and Hikaru, not as Prince and Knight.