Here's a quick list of my favorite MashMorgan fics :3

Humor

Rekindled Fire.

Guda/Morgan and Mash/Morgan. In which Morgan has recovered SOME emotional range, but "shame" is not in it. Sends me in stitches anytime I read it.

Double Trouble Boil and Bubble.

In which Tonelico and Morgan are fighting for Mash's affection. Absolutely fucking HILARIOUS to see them both getting super competitive while also blatantly thinking that the other is cringe.

The silver shilder symbol from FGO

Mash being Not Fucking Normal about Morgan

Hold me fast and fear me not.

In which Morgan accidentally hurts Mash while kissing her. They both have opinions about that.

Three Phalanges and Two Metacarpals.

In which Mash uses a catalyst to summon Morgan.

Pêsames.

What happens to Morgan after she dies.

The golden berserker symbol from FGO

Morgan-centric canon retellings

(Free from) Sin.

In which Tonelico goes Through It. Heartwrenching.

Branches of Ash.

A longfic on Tonelico's journey to become Morgan.

The silver shilder symbol from FGO

Other

dust to dust

nsfw, Mash and Morgan have weird inhuman sex.