Dan Blackmore

Dan is a former soldier, and a Master dispatched by England.
He served as a soldier for many years, and was knighted by the Queen. When he was young he made a name for himself as a sniper.
While the Royal Family of England is a part of the West Europe Plutocracy, it opposes the one who holds the power to lead the group, Harwey.
After hearing that Harwey had accessed Moon Cell, and that there was the possibility he might be trying to monopolize it, the Queen sent her most trusted private soldier to the Moon. That soldier is Sir Dan.
Dan comes from an old family, and his body possessed magic circuits. Dan resented his magus blood, but one cannot refuse a direct request from her Majesty the Queen.
Although close to retirement, he was still a soldier, and thus he could only carry out his duty to the end.
With this, he went through one year of training and adjustment, and became a spiritron hacker. At the ripe age of 60 he was a late bloomer of a magus.

What Dan desires from the Holy Grail War is to be able to fight as a “Knight.”
While he has already received the title of Sir, he is a soldier who has crossed many battlefields. He came to lose many things through the battles in his past.
His ideals, his wife, and the life he imagined for himself when he was young. All of it burned away by the fires of war.
After living his life as such, all that he would be rewarded with was the end known as retirement from military service.
Dan greatly desires a clean separation between battle and everything else, and he only wants a clean fight. And now the Holy Grail War has presented itself as his last chance to be able to fight as a Knight.
Dan Blackmore suggests the importance of conviction to the protagonist.
The old solider speaks:

“Even if you have regrets, you should never use them as an excuse.
I did my best while on the path that I was presented with.
No matter how warped or crooked that path may be,
I continued to represent my own soul.”

Despite killing many a foe, and losing his wife, when Dan takes a weapon in his hands, he is under no illusion.
After taking up arms, you must bear responsibility for your actions. This goes for both the enemies you killed, and you who chose this path yourself.
To the protagonist who had not yet discovered the reason and meaning behind fighting, the old soldier compassionately sees him off.
Only at the very end are the mistakes you are responsible for brought into question.
Until then, you have no reason to stand still.
For that is the story of another certain knight I know too well.
To the protagonist whose memories still haven’t returned, and who holds but a vague desire to obtain the Grail, these final words from Dan were like those of a proud father.

Fate/EXTRA Material: Encyclopedia of Fate/EXTRA