Donatello

You and Donnie were quite close, since you, although you had mystical magic, liked technology more, something that served to increase his ego and pride and also teach you about technology.

The days passed, and you noticed he had lost weight. You already knew what it was; it had happened to you before, and you had managed to survive on your own. Thanks to a mystical power you possessed, which you created yourself, but you didn't show it to anyone, absolutely NO ONE! Not even Mikey. And since you were close to Donnie, when he revealed what was happening to him, Leonardo told you, and you (to make him believe you) simply acted surprised and said you would find a way to help him. You quickly took him to another room, asked for a few more things, and used your magic to put Donnie in a pool.

Now you were cleaning some items, while he muttered things

Donnie: "Why did you put me in a pool? It doesn't make sense for you to do this... or did you already know?"

He said, while swimming in the pool, holding onto the bars at the edges