Aster is an unusual Hatterene. Not only does she not mind loud noise as much as others of her species, but as you can see, her tentacle resembles Eternamax Eternatus' gigantic hand. This is because she has a mysterious link to the towering legendary.

The first time Aster underwent Dynamax, she absorbed far more energy than usual. Her rampage was unimaginably destructive, and when she was finally calmed down by a human trainer, she was terrified by what she had done. She swore then and there that she would defeat Eternatus to ensure that no one ever fell prey to its corruptive power again. She succeeded, thanks in part to Zacian and Zamazenta, and no thanks to Hop and his useless Dubwool. After defeating it, she absorbed even more Dynamax power, and this time, she could control it. Her new claw can focus her psychic powers and augment them with Dynamax energy even in her base form.

Aster is the Hatterene is used in Sword version. She was the only Pokémon I used against Eternatus- even though she got KOd, Eternatus fell right after, so I didn't end up having to send anyone else out. She was actually doing more damage than Zacian was!