https://www.dlsite.com/maniax/work/=/product_id/RJ01208226.html
https://www.dmm.co.jp/dc/doujin/-/detail/=/cid=d_397872/

>I'm staying with my brother and his wife. One of my roles is to help my sister-in-law and look after the house while my brother is away on business. One day, when my brother goes overseas and we are alone again, I accidentally witness her masturbating... I can't contain my excitement and sneakily pick up her shorts from the laundry, and there it is...
>"...That's my underwear, isn't it?" "You're a boy, after all, so it's inevitable when you find underwear like that."
>"It's gotten to this point... I wonder if you've been pent up for a while?"
>"Don't run away like that , it's fine." "It doesn't seem like this is good, Rikuto..."
>"Ah, come, hmm, don't be shy, come on, hurry up!"

Base +20, your_name +6