After Arthur passing out. Gilgamesh sighs is disappointment.

Gilgamesh: Enemies we may be, but I'm not a cruel ruler as you are.

Gilgamesh carried Arthur by his abs. 

Gilgamesh: I don't want to raise suspicion...

Gilgamesh's armor clangs around the halls as then Mei and Kiana came back with Gilgamesh taking his body

Kiana: What did you do to him?!

Gilgamesh: Hmph... Accusing me of such acts... I have come to assist you yet you treat this way. You both cannot kill me either way. Treat this man or else he might loose his life

Mei: What?! You-

Gilgamesh: Try killing me, and you're dropped dead. Mongrel...

The captain then came

Gilgamesh: So does the Faker here too. I came not to fight. But you better look at me before I stab your back

Shirou: I know... Archer, give the body to the girls and I'll bring you in with the plan.

Gilgamesh: Heh... Making friends with enemies huh

Shirou: The enemy of my enemy is my friend. That is for now...

Gilgamesh: Gotcha

Gilgamesh drop the body and walked towards Shirou. Gilgamesh the tested him as golden portal quickly fired a weapon only for Shirou to just deflect it with his Muramasa. Taking the weapon it was a dagger used by EMIYA

Shirou: He's with us too. But Rin and him will be patrolling the Fuyuki if anomalies are happening. It seems that it's not just Fuyuki city either it's the whole entire world

Gilgamesh: I see

Shirou: Come

Shirou then walked around as the girls were confused how he just let him go. They quickly went to Arthur's body. It's pretty much weakened beyond restoration. Except they do sexy things. L-l-l-l-l-l-lewd things. Yet the girls don't know about it just yet. 

Quickly Mei and Kiana take Arthur to the sick bay room. Professionals quickly checked him giving the result of physical weakness. That's it, he's very weak due to lack of mana. 
________________________

???: Is that so?

Theresa: Yes...

???: Great that he's being a good boy

Theresa: Quite weird you said just now

???: Can I see him now~?

The white haired woman... ahem Caster-oneesan stood up as Theresa then guide her through. Both women if you can even call Theresa one, talk with each other making few giggles and such like old people talking. 

Theresa: They're not here...

While trying find them they then bumped into guys that being Shirou and Gilgamesh

Shirou: Who the hell is that?!

Theresa: She came with us though...

Shirou: I don't remember

Merlin: Well you must have forgotted about it captain. I'll introduce myself again... I am Denise

Gilgamesh: ... Are you out of your mind

Merlin: Precisely, yes!

Shirou: Theresa the survalance camera didn't see her except she just walked into. Some hall ways also she wasn't in the hangar either

Theresa: What?!

Gilgamesh and Shirou prepared themselves for a fight as they know that this woman is a heroic spirit herself

Merlin: *sigh* You got me

Both attacked the woman but only their projectiles and attacks were futile. Not to mention it is a tight space. Merlin just catched them all while not feeling anything

Merlin: I'll introduce myself then... I am Merlin, caster class to be exact.

Shirou: How did you get here, and why are you here?!

Merlin: Hmm... I just got here a moment ago... The grail was calling me so I took this opportunity but... it's strange that I spawned without a master...

Shirou: You're new

Merlin: I feel a familiar presence here so looked into the rooms and guess who I just noticed

Gilgamesh: Arthur

Merlin: Correct~!

Shirou: How did you know?

Gilgamesh: She's Lady Avalon, a grand caster. One that trained Arthur

Shirou: How come did I not know this...

Gilgamesh: ...Just let her pass for now

Shirou: But she's an enemy

Gilgamesh: Let her be, Faker

Shirou sighs as he unsheathe his Muramasa

Shirou: If suspicion break out we will do everything we can to kill you that also applies to you, Archer

Gilgamesh: Sure

Merlin: Alright then, so where is my Baby nephew~?

Shirou: They're at the sick bay

Theresa: Alright then... 

Theresa and Merlin quickly left the two as they then head to the sick bay. Shirou still display caution for the Servants or I should say Heroic Spirits on board with Arthur being an exception. As the old hags finally arrived. Merlin quickly came to Arthur just as Mei and Kiana is quick to be alerted, although Theresa is cautious. She walked to to them and discuss what just happened

Merlin: Oh my... My poor Arthur... Weak and lacking of Mana. Girls please leave this to me!

Kiana: First of all no! 

Merlin: Shut up I've been waiting for this moment to come!

Theresa: Merlin, What are you doing?

Merlin starts undressing

Mei: Oh my...

Kiana: Hey, stop that!

Merlin stops undressing as she smirks...

Merlin: Hmm~ My my~ Are you jealous of me, girl?

Merlin referred to Kiana

Kiana: W-w-w-w-what??!?!?! n-n-n-n-no!!!! N-n-n-not at all!!!!

Theresa: Merlin you still haven't answered me

Merlin sighs as she pouts...

Theresa: Are you just that horny?!?!?!

Merlin: Yes... and no...

The girls may be surprised but they are also surprised in the fact that Merlin said no.

Theresa: What do you mean?

Merlin: Ok you know what. I'll let it off the hook. Intercourse do increase mana for both partners

The girls quickly blush as Theresa was just urking towards the girls. Disgusted by them being blushing.

Merlin: I mean I can do it... But I'd let the beginners do their job for their comrade~

Theresa: No! Just no! Please no!

Merlin: I'll make sure that there will be no child made~

Theresa: Just no! Kiana isn't at the legal age just yet

Merlin: It doesn't have to be like that~

Theresa: Just please do it yourself

Merlin: Augh! I'm too bored, It feels like I'm weakened that the girls need to do it for Arthur~

Theresa: You-.... Alright fine! Fine!

Merlin: Ehe~

Theresa: Don't ehe me!

And thus. Merlin grabbed the Old Hag that is Theresa out off the sick bay. Kiana and Mei just looked to each other. It's either Arthur or they loose him completely.... Oh boy... The doctors there prepared pills and condoms(Wonder how did it got there)

???: I'll leave this make sure to have a safe seggs~

The physician left the sick bay.  
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Welp it seems like the Lemon got in here you might need to skip but the seggs is important for the lore, I did a little work so let me do another break hehe. Also I changed a bit from the chapter 5 so do check it out if you will