I recommend Lucis Crystal Treatment.

Thick treatments or hair masks can feel heavy in the summer, but Lucis Treatment has a watery texture, so it's great for a light treatment! If you use it consistently, your hair definitely becomes softer and the texture feels different! It isn't sticky, so I recommend it because you can keep your hair calm and tangle-free even after use.

(It is even better if you apply hair essence after use.)