Undoukouen no Mitsushima-san

A salaryman undergoing a midlife crisis randomly attempts to do some pull-ups at a playground after a late-night drinking session. There, he meets Ms. Mitsushima, who ends up being his unofficial life coach and personal trainer. But when his erectile dysfunction is seemingly cured after months of beefing up, Ms. Mitsushima decides to take their relationship to the next level.
(Source: Irodori Comics)
Note: Released at Comic Market 101