Right in the tailpipe

With how she was laying - her hips flat against the seat of the bike - getting to her pussy was difficult. However, her ass was pointed right up at him. A perfect target.

So Ren stepped off and positioned himself right behind her, dropping his pants again and thrusting right into her plump ass.

"Bffft! Bffft! Ptuh! Ptuh! Ptuh!" she began to grunt, mimicking the sounds of a sputtering engine. After all, to her mind something was getting stuffed into her 'tailpipe'

Ren continued to thump away at her, with Makoto continuing her sputtering over and over, until eventually he blasted his load deep into her ass.

"KACHRRRRRRRRrrrrrrrRRRRRrrrr" she started to groan. Seemed like 'lubing up her tailpipe' wasn't the best for her 'engine'

Either way, he circled around in front of her, seeing her eyes rolled back as drool dripped from her mouth. Even in this mindset she couldn't prevent the orgasmic result.

"Makotorcycle, reset your mind. Ignore the issue with your tailpipe" he commanded.

Makoto immediately straightened up, now making her usual engine idling sounds again.