Inspired by self-insert Fate crossover fanfics. I thought I could do a mini-project with this.
I do not own Fate or DxD.

Waking up in a dark place, where I yet to let go of my dreams. I slowly wake up my eyes, till I see not my room. I started to freak out a bit and get my blood running into my brain. I hastily got up and quickly observe the area around. This place isn't normal, that for sure. The space all round me is purple and moving very slowly. I can't tell whether it is a wall or endless space, am I standing on anything?
"Where am I?" I ask to the empty space around me.

"Ah, I see that you're awake." I voice said behind me

I turn around to see a old man. He was wearing a dark outfit with white gloves, a cane in his hand. His face seem similar to that one troll from a Fate anime I watched one time before.
"Who are you?" I questioned.

"I am Kischur Zelretch Schweinorg" He said.

The name 'Zelretch' hit a ding and my mind started to repeat Zelretch name over and over. The answer came into my head, 'Zelretch! The dead apostle and wielder of 2nd magic.'

"Zelretch the one who trolls and prank people using dimensional magic!" I called out.

"Ah yes, a lot of people who call me troll or a prankster"

"Am I dreaming or something?! I mean you're not real, you're a fictional character from the Fate series." I exclaimed out loud.

"First take a seat and calm yourself" Zelretch pointed out a chair that wasn't there when I looked their before.

I sat down and controlled my breathing into normal levels. It's difficult to calm down. Something that comes from a supernatural anime could never happen in real life. Yet here it is, Zelretch in flesh and blood, sitting across from me.

"How is this possible?" I asked.

"I think you already know the answer to that" He said.

"... Kaleidoscope" I answered my own question.

"Excellent, I knew your analysis (otaku) skills are great, Yoshiki." Zelretch said with a simile on his face.

"How-"

"Did I know you name. I know much about you." He said.

"That's creepy... So, where is here?" I asked.

"Where we are, isn't important. What's important are these?" Zelretch took out 7 cards and showed them to be.

"The class cards!"

"Correct, one of each class."

Saber - Servant of Sword. Best overall Servant. Agile and powerful melee warriors. They also have a Riding skill as well.
Archer - Servant of Bow. Best scout. Proficient with projectiles and attack from a far.
Lancer - Servant of Lance. Very agile and skilled with long-range melee weapons. Use hit-n-run tactics.
Rider - Servant of Mount. High Riding ability and powerful Noble Phantasms.
Caster - Servant of Magic. Greatly skilled in magecraft and have a Territory Creation skill.
Assassin - Servant of Murder. Have the skill to conceal their presence and attack stealthily.
Berserker - Servant of Madness. Very dangerous rage warriors. Enraged by Madness Enhancement, which gives them more power in exchange for sanity.

"No extra or other Classes?" I asked

"Not this time. Pick one card." He said

Before I could choose a card, I knew something that Zelretch would give out so easily. "What's the catch?"

"Quite observant of you. The catch is that I need you to explore this dimension, where demons and angles still exist."

"A dimension where the Age of Gods has yet to ended. Why do you need me, when you can go yourself using Kaleidoscope."

"Well, there's a dragon making it hard to cross to that dimension. He's called Great Red."

"Great Red!? The Highschool DxD's world?!" I somewhat yelled.

"That very dimension." He smiled

"I'm guessing you won't be accepting a no for a answer." I sigh, then look at the cards again.

Which card will serve most useful to me.
Berserker is out of the picture. I prefer to retain my sanity. Rider class I don't like very much, plus using a mount Noble Phantasm will cause to much attraction. Assassin seem good being able to hide from the world, but not highly combat effective against powerful opponents. Caster is good at making a defensive home using Territory Creation. Many characters from DxD either fight up-close and/or use magic, guessing Archer won't be effective unless I get EMIYA. Lancer is very quick, so I can travel around or escape quickly from battle. Saber is balanced and have good Magic resistance.

"I choose Saber" I told Zelretch.

"I see, playing it safe, uh." He said.

"I rather not risk it."

"Alright here, I'll place it inside your body so you won't ever lose it." Zelretch places the card on top of my chest and the card slowly phase through my clothes and skin. "I guess you already know how to use that card"

"y-yes" Remembering the Fate/Kaleid Liner anime.

"Now let's get you over there"

"Wait didn't you say you had problems getting there, also where am I gonna live without money.""I know a way, first stand here." He said and I stood on the location.

"I know a way, first stand here." He said and I stood on the location."Take this Gem" He gives me the gem. "This will create a backdoor for me to enter the dimension. Once the door is made I'll give you the cash you need."

"Take this Gem" He gives me the gem. "This will create a backdoor for me to enter the dimension. Once the door is made I'll give you the cash you need."

"Ok" Agreeing to revive the money later on "but that doesn't answer the first question."

"I'll sling shot you cross Great Red's territory without him noticing you."

"Wait whaaaa-!" A vortex rift open underneath my feet and sucked me in."Zelretch!" I yelled before my body feels like speeding passed mach speed.

[Moments later]

I was free from that horrifying acceleration through dimensional space, but still not safe. I was falling. Being pulled by gravity and air pushing against me. I was like miles above the ground, seeing the land and ocean from a great distance.

And thus, my adventure began.

Anyone want to take a guess on which Saber spirit will I get?

I decided to rewrite this crossover with a somewhat original heroic spirit.