Set in a Onsen inspired by the lower pool of Liard HotSprings

Danja embarrasses Alta by mentioning that Alta has a crush on Twadi."Hay Twadi, Alta here has a crush on you." 

Alta: "Oneesan?!"

Danja massages Alta's genitals while encouraging him to 'go for it' with Twadi. "I beautiful woman nude in a romantic onsen. Now's your chance Otouto. Go for it!"

Danja lays Alta down on the edge on the spring goes to get a towel. and leaves Twadi to finish Alta off.

Danja lays Alta down on the edge on the spring goes to get a towel."We're going to need a towel. Twadi do you mind?"

Twadi takes Alta's erection in her hand and strokes inexperencely 

Alta should to be tall enough so that his muzzle to be the same level of Twadi's breasts. What do you think?

I think Twadi would go  with it and feel admired that he likes her
But a little  unsure about how to masturbate a male.