Shards of a Memory / Heartwarming

"Angry Baby" by Uggables

General

Master Shard is generally more affectionate with her sons than canon!Splinter is. She licks their foreheads (which are basically cat kisses), she accepts hugs from them and gives each of them Affectionate Nicknames, something she extends to April and Casey.

Conversely, while the canon!Turtles usually relegate to referring to canon!Splinter as "Master Splinter", "Sensei" or (if in a particularly vulnerable moment) "father", here the turtles are much more informal, calling her "kaasan" (the informal, direct word for "mother") or simply "mom".

Chapter 1: Master Shard

The whole reason why Tang Shen decided to get baby turtles and named them after Renaissance artists was because both were things her deceased husband Hamato Yoshi liked.
Leonardo's first word was kaa-san. For English speaking readers that need context, his first word was basically "mommy." It was this that made her realize that she had a second chance at a happy life and a family with the turtles.

Chapter 2: Happy Baby

The whole chapter is just Shard playing hide-and-seek with Michelangelo, devolving into laughing, hugs and kisses.

Chapter 3: Clever Baby

Even though her record player was a relic from her human life, Master Shard is almost completely dismissive of it when the turtles don't respond to her calls, more worried for them than her possessions.

Chapter 5: Twitchy

While they are sleeping, Shard pulls Michelangelo's fist out of his mouth and undoes a stranglehold Raph has over Leo. Please note that they were toddlers at this time and suddenly this image is a lot cuter.
As a toddler, Donatello's curiosity extended to Shard's tail and would consistently try to pounce on it.

Chapter 6: One of Two

While April was angry at the turtles for her dad mutating into a giant bat, she was never angry at Shard and missed her greatly. By the end of the chapter, she is sobbing in Shard's fur over it.
April has come to see Master Shard as a mother, having almost no memories of her birth mother, even calling her "kaasan" as though she were.
April: I missed you, Kaasan.
Shard: Welcome home, my daughter.

Chapter 7: Creature Comforts

When April feels guilty about the mother/daughter relationship forming between her and Shard, Michelangelo gives a surprisingly profound statement about how having a second mom doesn't devalue what she had with the first.
Shard: My youngest son can be quite wise in matters of the heart. He surprises us all sometimes.
- Even better, April only had this conversation with him because his open innocence makes Michelangelo the least judgemental among his brothers, thus April can trust him with personal thoughts.
When Karai kidnaps April, Shard immediately goes out alone to rescue her. She knows it's a trap set specifically for her and it would mean saving "the daughter of her heart" from "the daughter of her blood", but she goes in anyway, not waiting for the turtles to return home or anything.
When faced with a Sadistic Choice — let April die to get Karai back or save April and lose Karai — Shard gives Karai a brief heartfelt recollection of a happy moment they had when Miwa was a baby before escaping with April, basically planting a seed of doubt in Karai's corrupted image of her before running off to save April's life.

Chapter 10: A Cat May Look at a King

After their harrowing fight against the Cat King, Mikey spiked Shard's tea with enough catnip to calm her down but not enough to repeat "that thing [they] won't mention in [their] house ever again", knowing that she would need it.
The chapter ends with a glomp, Shard reassuring Mikey that he is still her "Happy Baby."

Chapter 11: Till We Meet Again

The entire chapter involves Splinter and Shard meeting each other all over again.

Chapter 13: Angry Baby

Raphael's arc is all based on Anger Born of Worry, Raph essentially sitting by Leo's side while he's ill.

Chapter 14: A Shard of Time

While Shard tried to stay out of trouble, she only insisted on helping Casey when she say that she refused to back down against bullies wanting to rob his dad's store.
The chapter's epilogue reveals Shard saving him from bullies in his youth is what eventually inspired Casey to take up vigilantism.

Chapter 20: Together Again

While Shard is at first upset by the tag Casey left in her dojo, she completely forgets her anger when she recognizes his writing as the same as the boy she saved many years earlier.
While Casey Jones dismisses Master Shard as just another authority figure to ignore, he pulls a complete 180 when he realizes that she was the "angel" that save him in his youth and would later inspire him to take up vigilantism. He even takes the time to clean off the tag he left in her dojo unmotivated.
- He's also shocked when he realizes that the kids she talked about when they first met were the turtles he's fought with/befriended, and that she not only told the turtles about him, but that the key he gave Shard to get the food she needed is one of the family's sacred possessions and is regarded by the turtles as the "Special Key".

Heartwarming / Shards of a Memory