I’m buying it!

Seiji paid close attention to any sounds coming from Shika's room.

As he expected, he heard faint moaning. The sounds gradually started getting louder, sounding quite seductive and really stimulating his imagination.

How was he supposed to explain these sounds to Reo if she heard them…?

Luckily, the sounds finally died down before they got any louder.

Seiji was worried about Shika's situation, so he went to knock on her door.

There was no response.

He waited a moment and knocked again.

There was still no response.

Becoming even more concerned, he announced "I'm coming in" before opening the door.

He saw that his adopted younger sister was lying on her bed with a flushed face and tears in the corners of her eyes. She appeared to be asleep.