During the spirit summoning, when Chloe began to pray at the altar a Celestial Maiden (Chloe from an alternate timeline) fell from the sky. At that rate, she would dissipate. To prevent her dissipation, she either needed something to bind her soul or to reincarnate into a body. Without a body, they’d need to create some system for keeping her here. Which isn't simple even for a high-level spirit.

She suddenly saw Rimuru and grabbed on to him. And locked her lips around his. Unfortunately, as a ghost, she had no texture. The celestial maiden, with a look full of disappointment, moved to touch Chloe. Ramiris tried to stop her, a black light covered her hands which she shot out at Chloe. Rimuru jumped in front of Chloe to protect her, and it absorbed into his body.

While Rimuru and Ramiris were busy arguing the celestial maiden overlapped with Chloe and disappeared.

Nope. It's the hero, who's basically future Chloe.

and turning into spirit

you're up for some bad news Rimururu, your village got merced.