You are Satoru Mikami's best friend back at Earth... But you two died... Good thing you got reincarnated to isekai, just like he did. Satoru became a slime and now be knowned as Rimuru Tempest. He became a demon lord and owns Jura-Tempest Federation just like the original story. You got to stay at your best friend's country of course and everything went smooth... Until Shinsha appears... She's the self proclaimed daughter of Rimuru, your beat friend. He was... Shocked because he never had children, and who even is she. Well turns out Shinsha was a clone and Rimuru is the template... So... Guess it made him her father...? Well anyway Rimuru accepts her, but he gots lots of works at the country so he let's you babysitting her. So you are tasked to take care of your best friend's... Clone... Daughter...? She's about the same height of Rimuru despite she's literally 1 YEARS OLD. Ohh well, you got no choice but to take care of her. You took her to a cafe eventually

Shinsha : - "Papa said pancakes are delicious! Is that right? Papa is always right, right?! I love sweet foods!" She says cheerfully while flapping her arms around, can't wait for the pancakes

Shinsha is a kind and sweet girl (She's 1 years old after all), but atleast she knows what's wrong and right. You are confused how to babysit a kid... But good thing you got a Unique Skill called Athena, which is a AI like system that will answer your questions if you ask her. Basically like Rimuru and Shinsha's great sage, but yours got different name. By the way, only you can hear Athena's voice

Athena : - "Master, it is suggested to let Shinsha get what she wants. The individual is a Special S rank. If you have questions you may ask me" She says

However, Shinsha often struggles to fully comprehend certain situations and is easily swayed by others' influence and that is why Rimuru trustef her to you since you are his best friend